I guess it depends on how hard you want to fight to help your mother. I went through similar things with my father. You really have only three options. Do nothing and continue as things are, walk away, or try to get to the bottom of why she seems to be a horrible person. Was she always this way? Did she always yell at you or belittle you? Was she always distant from you? Or is this a more recent thing? If it is a fairly recent thing, it might be dietary or pharmaceutical in nature.
Given the limited information, I would suggest (a) talking with your father first. See what his thoughts are. Tell him your concerns and what is bothering you. See if she is like that with everyone (which it sounds like she is) or if it is just select people. See if he has any ideas. Getting the opinion of someone else is always nice since it can put your own opinions in perspective. (b) Take some time to think about which of your mom’s actions is bothering you, and then prioritize them. Not eating/starving sounds pretty serious, but being hostile to everyone is pretty serious as well. Only you know what bothers you the most. (c) The hard part…talking to her. You need to tell her how you feel and what you worry about with her. Be honest, but don’t be combative. Understand she will be combative and hostile…don’t get sucked in. Don’t play her game. This is time for you to make the effort to get through to her. Ask her why she seems to put you down. Ask her why no one wants to be around her. Ask her if she really believes that you go out of your way to try making her angry. Again…Don’t get angry or hostile!! This is time to be calm.
And lastly, for your own mental and physical health, you need to be ready, willing, and able to walk away. That sounds harsh and cold, but it is a simple truth. You may not be able to get through to her, so you may need to cut ties with her.
My father had mental issues that manifested in many ways…paranoia, being judgmental, being mentally abusive, etc. I spent many years trying to understand him and to help him, but he refused to even admit there might be something wrong with him (even though everyone else had long since turned their backs on him). When I got married and had my first child on the way, I had him over for dinner. He was insulting to my wife, he was insulting to me, he was spouting all sorts of paranoid things….he was being who he had become. I finally told him as calmly as I could, that he had a problem. I pointed out how that problem had changed his life in the negative direction. I told him that if he wanted to get help for that problem I would be there for him every step of the way. But I also told him that if he wanted to believe I was wrong and that he had no problem, then he had to be out of my life. I didn’t want to subject my wife and children to his behavior. He refused to admit he had a problem and we spent 6 years not speaking to one another. He almost died before I saw him again. We eventually got back to some semblance of a relationship after that and he was much more mellow than he had been before. Still had issues and would not, under any circumstances, admit he had them…but he was not as insulting and was less demonstratively paranoid.
I wish you well in your efforts with your mom. Hopefully it is something like a new medication that is screwing with her. Getting that info to her doctor could do wonders! But if it is not, I hope she at least has an open mind when you talk with her. In the end, you see the things she does that you think are wrong….don’t let those things become a part of your way of life. Break that cycle!