You tried to help her apply for Medicaid. That is the logical thing to do. You have been saying she's both stubborn hoping you will cave and crazy. Could your family (you and your siblings) have her committed for psychiatric evaluation? Maybe your state might do something. Molinit is right, if asked, you need to tell your state that you are unable to help.
You've gone above and beyond by doing more than most children would do. I'm sorry she still is so toxic for you. Like everyone is saying -- don't cave. You have to save yourself first. I know it is hard because you are so sweet.