How many years do people stay in stage 5? Is it typical to be combative?

I post here whenever I have hit rock bottom.

My MIL has been in stage 5, moderate for a very long time. She has been living with the disease for at least 8 years now. She spends 5 months each with us and my husband’s other sibling. The only thing she does is curse me 24/7 either for the food I cook or that I am stealing her clothes. Even if I have cooked the best tasting food, it's horrendous for her, she says SHE makes it way better. If it's freshly cooked, she says it tastes like it's three month old. If I make the right consistency, she says its not cooked but if I cook it longer for her, then it's overcooked. It is so ANNOYING. I am losing my mind. she hates most of the meal options. We cook everyday dreading what yelling we will encounter. Being at the dinner table is a nightmare. Actually being in my house is a nightmare. I feel like running away. Even while I am working from home, she constantly bangs the cupboards, doors and yells loudly (about clothes stealing). It disturbs my work having to hearing this even when I am locked in my room. It affects me mentally, even though I try to shrug it off as the “disease”. She is physically very healthy and active for a 82 yr old inspite of the uncontrolled diabetes she has had for 40 yrs (no heart disease, pressure or any diabetes complications). She never moves her butt to help me and I am the one who does the cleaning, cooking, laundry and upkeep of the two washrooms she uses (which are so filthy). My husband sometimes helps with cooking and he takes care of the medications, but he is honestly scared of her. All she does is curse (not swearing but real curses that evil things happen to me or that I should get a disease and die, let someone shoot you, something fall on your head, let your kids illtreat you, etc). Even in her sleep I can see her cursing me, that means even in her subconscious mind, it's me.  She has now started cursing my 10 yr old son. She does not curse her own children, it's only the in-laws and some grandchildren. Even in the daily evening prayers, I can see her praying to God to punish me and to make me suffer. She takes insulin several times a day yet loves carbs and if we don’t give her what she wants, it's constant tantrums that are sometimes scary. Since we hid the sweet stuff, the only thing she does throughout the day is rummage through the house, every nook and corner. It is so annoying. She also hits the washroom like 50 times a day (it has always been like that, not any UTI). Her routine is drink water, washroom, drink water, washroom and the washroom, no matter how much I clean, gets dirty in 2 days. My problem, is that I am burned out, depressed and it's getting to my nerves. Sometimes I break down and yell but then its 10X times the yelling in return so I just stop because there is no point. I cannot win against her. Especially with an unsupporting spouse who remains quiet during her yelling. We are from South Asian culture, so a nursing home is not an option. I will have to put up with this until the end. And I sometimes feel I might go before her because of the constant curses. I also feel that my personal life and career are not working out as a result. Wondering if it is the curses. She has been in this stage for nearly 5 years. How many years do people stay in this combative stage?