You don't really have to distance yourself as long as you stop her from saying things that trigger you. Tell her what the rules are (like no talk about weight), and then stick to controlling it. You need to train her. And I guarantee you that she will start treating you with more respect, and you will feel a ton less fragile.

I'd recommend that you do whatever it takes to get rid of the symptoms. They are torturing you day and night. You have described how unhappy you are, that you can't take it anymore, that the voices won't leave you alone, the paranoia is constant, and you have times where homicidal/suicidal thoughts scare you. Fat and an absence of that tortured existence sounds peaceful.