Mom keeps repeating to outsiders how great she’s being taken care of?

If you feel that sister is not caring for Mom, then call Adult Protection Services. Not so much to report Sis but to see if Mom could be evaluated. Tell them everything you have done for her, Sis seems to feel Mom does not need. An evaluation will help you in dealing with Sis.

Does your Mom have a medical diagnosis of cognitive and/or memory impairment? I'm asking because if she does, then what she is telling you may not be accurate.

We experienced this with my MIL who, unknown to us at that time, was having memory issues and gave all 3 of her sons a different version of the same story and they only figured it out when they got together and compared the stories, unintentionally.

Just saying this could be what's happening and not your sister's fault.

FYI Meals on Wheels food... my MIL wouldn't eat it, but maybe taste and quality depends on where you live.

Is your sister the PoA for your Mom? You wrote in a reply:

"Mom lives alone and the sister who watches over her has taken all of her money to the point where mom says she wouldn’t steal from me. And I would think why would she even say that until I saw the bank statements."

So, does your sister have receipts for what your Mom's money is being spent on?

I'm guessing that the fact that your mom is still able to live by herself in her own home(though she probably shouldn't be)that she does in fact believe that she is well taken care of.
And if she has any kind of dementia, the fact that she tells you that she still hasn't eaten at 8:00 p.m. doesn't make it so, as she may have forgotten that she just ate 2 hours ago.
It's probably time to sit down with your sister and decide what needs to be done next as far where your mom should go.
To me it sounds like it's way past due that your mom should be in an assisted living facility, where she will be around other folks her own age, have lots of activities and 3 meals that will be served daily at the same time.

Your mother getting out of breath walking to the bathroom is not your sister's fault.

Maybe your mother is content because she's being well cared for.
Every senior does not have to eat dinner at 5pm every day.

I was an in-home caregiver for 25 years and now have my own homecare business. So I'm going to tell you from experience what to look for to know if your mom is being well cared for.

1) Does she smell bad or appear dirty and unkempt and in dirty clothes?

2) Is she living in filthy, hoarded, or dangerous conditions?

3) Is she losing weight?

4) Does she have unexplained bruises or injuries?

If you answer 'no' to these questions then your sister is adequately caring for her or even well caring for her. Dinner sometimes being late does not mean she isn't being taken care of

So instead of offering to set up Meals-on-Wheels which in my experience the food is absolutely disgusting why not commit to bringing dinner for them both a couple times a week? Instead of offering to arrange visiting nurses who for the most part are useless, why not try asking your sister what she wants or needs.

Let her tell you what she needs and how you can be helpful to them both.

I find in my long experience with homecare that the number one thing a caregiver dealing with seniors wants is time.
They want a break where someone else comes and stays for hours at a time so they can have some life to themselves.

Make your sister this offer. That you will personally commit to 'X' number of hours a week so she can have time off.
Or offer to take your mother to your house on weekends to give your sister weekends off.
I'm sure she will be very appreciative of this kind of help. Most family caregivers are.

Do you have a question for us, or just needing a bit of a vent? Because vents ARE needed or we explode from the buildup of steam. This is just kind of typical. It's good to know that mom has some good things to say to some people some of the time.

Mom is showtiming. She looks good for outsiders and can look bad to you. Have you talked to your sister? ALZ confuses people. My daddy did that to me. I was the worst daughter ever! But he wasn't malnourished, bruised, in the hospital everyday, he had clean clothes, clean bed sheets, clean house, bills were paid---but I was the worst daughter ever - until about a month before he died then I became the best daughter ever! I love him dearly and still do! Would I change the last year of his life - NO why because I share my experience with others and I understand what others are dealing with. ALZ is very, very, very challenging and need to remember that person is in their own world that is nothing like ours. Prayers for you!