Where does the strength and will to continue caring come from when Mom refuses to care for herself?

My Mother is only 73 but she has crippling arthritis, osteoporosis, a knee replacement she never done the therapy for, but mostly depression. Mother has lost everyone in her life besides me. Her firstborn, her parents, both husbands and her only sister. When my sister (her bestfriend) died in 97 she grieved for 3 years heavily. My step dad was alive then and helped her through that. 5 years later he died with cancer. She grieved but not as much due to my 14 year old son moving in with her. He was always her boy anyway haha. Long story here so bear with me. After a life threatening accident and doctors feeding me oxycontin for 1 1/2 years I became addicted to pain pills that eventually turned in to a meth addiction (4 years clean today) which landed my daughter in the home with her. I finally asked God that if he couldn't take it away to just kill me and i was arrested and locked away from home for 2 years. My daughter got pregnant and I returned home 2 days after the birth of my grandson to find Mom just not doing so well. She just out of the blue stopped coming out of her room, stopped going to town, She simply STOPPED MOVING. I realized that the statistic ulcer which she has had since she was 32 had busted open again bigger and deeper thab ever. It's on her ankle so this was the reason for the mobility issue. The problem is that the ulcer has been healed for a year now and she still refuses to do anything for herself. I tried everything. Tried getting her to have coffee on the porch, to take trips to wal mart she could ride the scooters, uh tried getting her to sit in the living room ,I tried everything but she falls back on it hurts to bad to be mobile. So i go and get her a wheel chair, a scooter was donated, she has a walker, a cane etc.. No reason to be sitting around waiting on me to wate on her hand and foot anymore. I tried telling her she is loosing what she is not useing and if she would use it it would hurt less everytime but she refuses. The dr.s said to stop cooking 3 meals a day for her so i did...She has lost almost 100 lbs in this last year. It is depression. She refuses to tell me what she needs because she says she doesn't want to be a burden but evidently she does or she would get up use the wheel chair to pop herself a bisquit in the oven and wait on it to ding. Her finances... Oh I just do not know what she is doing with her money but we are about to starve. I mean i am paying her to live here(which i think is wrong) and she still expects me to buy the groceries. She makes triple in a mth than i do on my disability. I have rambled on so long i'm not sure where the question is but it's only me to care for her and i love her but she takes me for granted and acts as if I owe her . I do it all at Mom's housE AND PAY HER TO LET ME DO IT! Feeling drained, taken for granted and o verwhelmed. God knows I love her but I do not like her right now. She can help herself she just simply refuses to. The equipment is here and i do 99% of everything. How do I make her realize i'm almost 50 not 21 and she is taking advantage of me?