I don't know what to do. My SIL is semi-capable of taking care of her own hygiene, cleaning up after herself and her dogs, but won't.

Maybe she's depressed, not just lazy

There is some important information missing here. I see that Countrymouse asked most of the same questions I was wondering. There is clearly something going on with SIL that is far more complex than "laziness". Depression came to my mind first, but I suspect many more issues going on with her emotionally and, maybe, developmentally.
As others said, your MIL asked for her to be cared for some years ago, so there had to be reason for your MIL to think she wasn't capable.
Pretty soon, she's going to HAVE to either move in with you or move into a facility. The dogs might have been helping her motivation but it's likely their own health is failing, both because she's neglecting them and because of their age.
Is anyone taking them to the vet if/when needed?
A primary care doc can put in an order for her to go to a rehab facility, but if she's seeing specialists, they don't have the time or inclination to get involved in behavioral issues or complex family matters.

I have a disabled nephew. Besides some physical disabilities he has a neurological problem where he doesn't rationalize. With 4 rods in his back for Scoliosis he is not suppose to gain weight. He now weighs at least 250 on a frame that can't support the weight. At 29 he has a fatty liver and has been told it could kill him. I have told him, I will not push him in a wheelchair. He can't walk 20 ft without huffing and puffing. Yes, I could worry but it just gets me upset. There is nothing I can do. I will never get guardianship. I am almost 70 and just can't be responsible for someone who says "Yes Aunt Jo Ann" and then does what he wants.

So, ur SIL needs to do for herself. I would do nothing for her. Maybe if she has to do for herself, she finally realize she has to lose that weight. Neither u or ur husband can do anything. And if u do u are enabling and making her situation worse. I am big on, I will help you find the resources, even drive you there but the rest is up to you,

Looks like a 50 yr on and off friendship is now done. Why, because I got a nasty phone call accusing me of not keeping her in the loop about some luncheons supposedly given by our class. I returned the call that ended up going to a FULL voicemail. ( can't get messages if ur VM is FULL) I texted and told her I had no idea what she was talking about and her VM was FULL. She has a cell with Data so she can get to her emails and FB acct where info on our class is posted. This was two months ago. I found out what she was talking about, her info was wrong. Two of her friends know the truth but she has not called and apologized. I am tired of pointing her in the right direction and being shot down. There is always a reason why she can't do it. Well, I can't do it for her. I really believe that God helps those who help themselves.

You both need to sit down with her and ask her if she even wants to get better. It's her life, her body, and ultimately it's her choice. Some don't want to get better because of shame or guilt about how they look or feel. Getting healthy and fit from a point of being morbidly obese is a long hard road out of hell. I was overweight once. It took nearly two years for me to lose 60 lbs. I've been able to keep most of it off for over 5 years and build muscle instead. But I did it because I wanted to do it. Your SIL has to decide for herself if she wants that. Otherwise you can't force her to change. Let her know your worried about her and you want to see her happy. Maybe they'll help her move forward.

I wouldn't put any great hopes on Friday's doctor visit changing anything.

How often is someone going over there (30 mins. away) to help SIL? I take it she doesn't drive. How does she support herself financially? Does she have the funds for Assisted Living?

Are you (and/or H) cleaning her place up for her? Helping her shower?

I asked these questions before (and I'm asking again), because I'm trying to get a fuller picture of just how much SIL depends on your H (and you) to survive.

How is her diet? Is it just too much (relatively?) healthy food, or is it lots of junk food? Do you take her food shopping, or is she ordering from the Internet?

So your SIL was already in a bad way before your parents-in-law died, and since then things have gone from bad to worse. And that's over the course of, what, fifteen years or so?

Would you mind going back a bit, to what might be at the root of all this? Her parents were concerned for her welfare: does she have a learning disability, chronic mental ill health, other medical conditions in the background?

You and your husband need to work out what to do, without any reference to whatever his parents said to him about ‘caring’ for her. Firstly, most people's parents would want us to care for everyone in the family, and for their son this ought to include you and their grandchildren as top of his list. Secondly, it would have made more sense for them to ask SIL to care for herself. Whatever they did for her while they were alive, it wasn’t a great success in terms of SIL’s health and well-being. There is no reason for them to leave it to your husband to sort out anything they may have failed at. They obviously knew that ‘caring’ wasn’t going to solve the problem.

It may be that there is some great new idea that solves SIL’s self abuse, or it may be that there is nothing you can both do. But DH’s parents have nothing to do with it, and guilt should not be part of your problems. This probably sounds like I’m cross, and I suppose I am – this ‘promise’ stuff is a lousy heritage.

So, did anyone watch the highwire act last night over Time Square? ? The brother and sister act walking a highwire. That was impressive. What was more impressive was the fact they sat on this wire with a long pole, and then got back up on their feet!

I didn't not realize how weak I have become, it is awful. I cannot stand up after sitting on the ground. I have to roll to my knees and pushup with my hands.."very graceful".

My friend just turned 70 and she just pops up -no issue at all. guess I will start doing chair exercises.

Maybe you can get SIL to do just a couple of chair excercises a day, and build up. I am going to after reading this and writing that.

Sometimes we have to let people fail to get them to move from the position they are in.

With everyone taking responsibility for her she really has no reason to accept it for herself.

Tough love is sometimes the only love that works.

Best of luck, my husband was suckered with death bed promises by his brothers enablers. It took 35 years before he saw how damaging those promises were to him. I personally think that no one should blackmail another with death bed requests, they are unfair and manipulative. I hope you all can find a way to get her to help herself.

I would not let her cancel this upcoming appointment, she needs to sign a HIPPA form for you, ask when you check her in.

I have a cousin that has been morbidly obese for most of her life and they just diagnosed that it was her thyroid. Doctors see obesity as overeating or laziness and often don't investigate the why behind the weight. You can advocate for her to ensure that her medical issues are addressed.

Could it be time for her to look into assisted living? If her life was wrapped up with her parents she is probably a bit lost without them. Not calling for help is a clear sign that she is not safe living alone.

I would let her know that you and your husband can not risk your backs by lifting her up and future calls will be dealt with by calling 911 for her. Sometimes we have to put our foot down and stop being a solution for our loved ones. As hard as it feels it is the kindest thing in the long run.

Tell your husband he only gets one back and ruining it because she has made bad choices is not a clever move. Encourage him to encourage her to move to assisted living.

It does not sound like SIL is living with you.
Just wondering who is buying food for her? Can that be monitored and that would force better diet.
If she is not caring for the dogs my inclination would be to contact Animal Control. Not only is it unhealthy for your SIL to live with animal waste it is unhealthy for the dogs to live like that as well.
If she refuses to call 911 for a "Lift Assist" and you happen to not hear the phone, the battery is dead, you are at the movies or any umber of reasons that is on her. Not your responsibility nor your husbands. Your SIL is an adult, apparently of sound mind so it is up to her to decide to make a 911 call if it is needed.
As far as the hygiene issue, if you take her shopping or out tell her that you refuse to go anywhere with her unless she has showered and has clean clothes. If you are going to visit, you do not go in if she is offensive to you.
You could contact Adult Protective Services and see if they would make a "Well Being Check" on her and if they find that her living conditions are not what they should be that might be a way to get something going to change the situation.

Your husband should not feel guilty. This is not of his doing.
Your husband may be feeling more embarrassed for her. (or possibly embarrassed by her. )

Could she be suffering from depression?

I don't think tossing out the word lazy about someone who doesn't look after themselves is really helpful, I think she sounds deeply, clinically depressed. Is there anyone who has the authority do be her advocate and speak with her doctor about what you are seeing - healthcare proxy/POA?

So, what happened in the end when she fell and couldn't get up again?

You and your husband must be going spare about this, but in comparable situations I've encountered - there really isn't anything you can do. You can get her medical advice, and therapy, and offers of help, and social care; and everybody will run round in circles for her doing whatever they can. But just as (I say this without meaning it to sound like blame) she got herself here, she's the only one who can start to get back again.

But one thing I think you can say with certainty is that she's long past the point where "lazy" means anything. She is morbidly obese, and she is now ILL. I know I've just said she's got to be the one to make anything happen, but that's why it's so hard. She's in too bad a way to do that.

Has anyone professional tried to work with her before now? - or have you lost count of the times... :/

Why does your H feel guilty? I'm not clear from your profile if SIL lives with you. How much help do you and your H provide her?

I hope you aren't expected to do the heavy lifting (no pun intended) with regards to caregiving your SIL. Who helps her with showering? Who drives her around? Who does the housekeeping (and cleaning up after the dogs)?