How do I not feel stressed out, worried, sad, afraid, angry, helpless at my mother's health deteriorating?

I agree with Grandma, but I would take this one step further.

I would tell mom that you are going to call a Hospice organization so that she can find out if she qualifies. If she doesn't want any treatment for "what ails her" then that is the next logical step.

Call around and find a hospice that is not for profit and set up a visit for later this week.

It's the compassionate thing to do.

What I am going to say may sound brutal.
Your mom has diabetes.
Your mom is choosing to ignore the doctor's recommendations
Your mom's health is declining due to these 2 facts.
Your mom is probably frightened that she will loose a foot or a leg if she is admitted to the hospital.
Your mom is probably frightened at the realization that she is not going to live a long time.

You feel stressed, worried, sad, afraid, angry and helpless for the very same reasons.
You would not be a loving caring daughter if you did not have those feelings.
The important this is that they not take over and consume you. You have to realize that YOU can do nothing for your mother but be there for her.
That said she is making decisions that directly effect you!
You need to tell her that.
I hate ultimatums but they are sometimes necessary to get your point across.
You could tell her that you are not going to stand by and watch her make poor decisions. If she is living with you tell her you will begin to look for Assisted Living or Skilled Nursing facilities for her. Or if you are living with her you can begin to pack up and look for a place. You love her but you hate seeing her slowly kill herself by not taking care of her own health.

Would she have stood by and watched you get sicker and sicker when you were little or would she have followed the doctors advice to make you well?

Another option and this would be a last option and this is far from easy or pleasant. Also this would probably destroy any relationship you have with mom.
Due to her not taking the doctors advice, ignoring her own health IF you can get a doctor to say she is not competent you might be able to obtain Guardianship and force her to get treatment. Courts do not easily take someones autonomy so it may be difficult. And guardianship is not easy.

One final difficult option.
She is slowly killing herself.
Tell her that you understand and while you do not like it you will stand by her and care for her.

I'd ask her if she wants to lose her foot? That is a real possibility when sores won't heal when dealing with diabetes. She sounds like she is in denial and if she doesn't think about it, it will go away. It won't. It can be treated without being hospitalized unless she keeps ignoring it. Unless it has turned into cellulitis and then that will probably mean she needs to be hospitalized. Cellulitis can kill her.
Sounds like it is time you talked to her like you would your own children. Be firm. Tell her she either lets you help her or you are walking away. I'm sure you won't walk away but you can let her think it. See if that attitude will make her come around to reality.

Since your mom is resistant to medical care, perhaps she would be more comfortable with a group that makes home visits. Landmark is a national company that sees patients in their homes. They have an office in Westborough, MA. In my experience, a person is more likely to be compliant with their treatment when they are less intimidated and overwhelmed with the process. I’m not sure about Landmark, but most at-home practices offer wound care and some other specialties as well. Either way, I wish you and your mom well. I understand how difficult this can be.

Do you have siblings? Are you an only child? She is scared. I totally understand that but doesn’t she realize that you want to speak to her doctor so she can receive the proper care?

DO YOU HAVE POA,,
DOES SHE HAVE DNR/POLST?

If you are not allowed to go into doctor office with her.. as she said,,, give her the phone number of the local taxi cab... Get to know the cabby's name and taxi number and his phone number... Keep mom in check and tell her you will schedule the taxi for her next appointment. You have too many things to do instead of waiting in the waiting room for her. She can pay a taxi cab to transport her.
Mom, if you don't want or need me in the doctor's office, then I really don't need to accompany you.

Sneeze,

She isn’t being fair to you. You have no idea what is going on. She is hiding information from you so she may be hiding it from her doctor too.

Okay, you don’t have access to her private medical information but how do you feel about writing a letter to the doctor as an extremely concerned daughter? Tell her doctor everything that you have told us. Expose her secrets. Tell him about her fear. Hopefully, they will respond accordingly.

I would insist that you would like to go in the office with her. Does she realize how serious diabetes is? Tell her that you are not taking her to the doctor unless she cooperated with you. She is manipulating you. Stand up to her. You deserve better. Obviously, you care about her wellbeing or you wouldn’t be asking for help.

What is her situation with her siblings? Are they close? Do you trust them? Do you want them to know her condition? I respect that you have respected her privacy but she needs medical care. Do you feel like they could influence her to get help?

What is going on with the irrational fear? Does she know others who have lost limbs due to diabetes? Something is triggering this behavior. Has she always been so fearful?

You say that you want to walk away. I understand that. She isn’t allowing you to help her. You’re just a taxi driver for her. This is a horrible situation for you. I’m so sorry. You don’t have to cooperate with her. You can tell her, either you are allowed to speak to the doctor or you are not bringing her.

Well, your do feel stressed out, worried, sad, etc... It comes with the territory.. You cannot help it, you love mom and don't want to see this happening.
ONE THING I WILL TELL YOU... DO NOT FEEL GUILTY.... PLEASE DO NOT THINK.. " IF only I did this, or I did that.." YOU ARE DOING THE BEST YOU CAN, AND IT IS NOT EASY... YOU ARE DOING WHAT YOU NEED TO DO... LOVE YOUR MOM... DO NOT FEEL GUILTY... \

If she has issues, easiest to check is UTI.... Start there.

First of all, I am so sorry that you are struggling with this situation. It is frustrating. You are totally justified to feel as you do.

Secondly, you mentioned diabetes in your profile. This is serious. She can’t treat herself. She needs the professional care of trained physicians. I am sorry that she is frightened. Fear is normal but she is putting herself at greater risk by trying to treat sores herself.

Do you accompany her to the doctor? Or have access to her medical records? Can you speak to her doctor to inform him/her of what is going on?

It’s obvious that her fear is causing irrational behavior. She is fighting you and other family members so I feel you need to enlist the help of medical professionals to educate her on caring for her diabetes and leading her to the proper treatment.

Best wishes to you and your mom.

I remember when my mom was slipping away. It was very difficult. Look into counseling,. They can help sort out things. (((Hugs)))