How do I set boundaries and not let her verbal abuse and attitude effect me day after day?

I was diagnosed with ms in 2006, and forced to resign from the medical field. In 2012, my mother was asked to leave her home shared with her sister. I have no siblings or other family. Her assumption was that I would automatically provide a home for her. Prior to her moving in, I had lived along for 18 years, quite an adjustment. I must say.
I provide 80% of her financial support including our home, etc.
My issues are that she is NEVER satisfied with anything in life. Hates that I “drug” her 45” away from her town. She hates where we live, has no friends, or hobbies. Mind you, She had none of these things prior to moving in with me. Her friends abandoned her because of her constant negativity and are long gone. The glass is always half empty, and nothing I do is ever good enough. No matter how much money I spend on her, compliment her, provide emotional support to her, it is still not enough. Remember, I have MS, yet I am the house keeper, yard maintainer, pet caregiver, etc., never offering to help out with anything. I know her tricks, she’ll do a chore or a minimal task, complain, scream and yell, and use profanities while doing it and then she’s pissed off for the rest of the day. I’ve gotten to the point that I can’t stand her attitude and behavior and will just do it myself, just to keep the peace and quiet. I know she knows I’ll say I’ll just do it.
Knows my buttons for sure. Then I’m pissed at myself for giving in and resentful of her just because. I feel like my blood pressure must be through the roof, and my heart is pumping a hundred miles a hour. I have undergone counseling for three years, read so many books on narcissistic mothers, meditation, yoga, you name it, I’ve tried it. I basically live on antidepressants and anti anxiety meds daily. And yes, I have talked to her doctor multiple times and he agrees that she is also depressed, but whenever he or I mention it, she is in total denial. It’s always someone else’s fault, never hers. I’ve told her many, many times that I am not responsible for her unhappiness, nor her miserable life she’s experiencing.
In her lifetime she experienced 3 miscarriages prior to my birth and she has actually told me, “You should’ve been a miscarriage too!” Wow, hard to respond to that!
I know that not every mother has motherly instincts and I believe she’s one of those, no compassion, care, or anything.
I have several really close friends that know my situation with ms as well as my relationship with her. She says she doesn’t like any of them (I’m 56 btw) so that is not really an issue, but whenever plans are made for the 12 of us to do something together as a dinner or an overnight camping trip, etc. she actually tells me that I am NOT allowed to go! So when I do go, I suffer the wrath when I return. She has not cleaned up after herself, creates indescribable, personal unsanitary messes that are left for me to attend to, dog waste, etc., I’m sure you get my drift. And of course there’s more attitude and name calling, etc.
Mind you, she is 82, but manages to go to the gym 3 days a week, shop, drive, etc., so physically she’s is able to care for herself.
My ms started to progress this passed July, involving a wheelchair, then rollator, then walker and cane. Thought I was through it until I dislocated my hip in October, and now am anticipating spine surgery after the first of the year.
She has actually told me, ‘I could take care of you, but I’m not going to because I don’t want to.” Simply amazing.

I do apologize for the long rant, I just seemed to have unloaded a lot of stored up anger!

I guess I’m asking for help with setting boundaries, that it’s okay for me to say no. How to let her verbal abuse and attitude not effect me day after day? It is so stressful and exhausting to deal with it on a daily basis.

Before someone mentions it, I can not kick her to the curb without her having resources. There is not any elderly discounted living that she would qualify for, besides, there is a two year wait list. There is no other family I can send her to. And although I am comfortable with my income, it is limited, so putting her in a home or assisted living facility is not financially possible. I will say that I have finally learned to worry about my own financial and future healthcare needs before hers. Of course she wants me to cash everything in to spend it on her!
Again, simply amazing!

Thank you all so much for any tips, advice, and personal stories on how you’ve handled similar situations is greatly appreciated!