I am so sorry you're going through this. I went through some fairly similar things with my mother. We were not close 9actually she hated my guts most of my life), but when it came time for her to require care, I put her in the best home money could buy. I paid well over the provincial monthly stipend allotted. Initially things were great. Lots of good food, great meals, treats, snacks.
Then, about a year in she began complaining that she wasn't getting enough to eat. We didn't really listen to her because she always had complaints and was often delusional due to her late onset psychosis.
We were wrong. She landed in hospital with a myriad of problems, malnutrition included. She never went back. They tried to charge me for 2 months notice. I went to the media, to the provincial legislature and to whoever else would listen to name and shame them. I was still practicing law at the time, so I think that also scared them a bit.
She was eventually placed in another facility that treated her very well until the end.
It's disgusting how many stories like this I hear. Sadly, eldercare has become big business and the clients are numbers. It's sickening to think that simple aspects of basic human dignity like having enough to eat are being denied to our elders.
Girl, make noise, make a lot of it. Some basic dignity and comfort isn't too much to ask for your mother's final months.