Speak to a local lawyer immediately and seek assistance. You may need to see if she can be admitted "against her will" to a mental hospital due to her threats. Or you may need to have her arrested for her threats, since they may constitute harassment. That way, the authorites can get involved and perhaps offer her some mental health assistance.
You may also want to contact her doctors to advise them of her threats so that everything is well documented before you seek to evict her from your home.
Then, move to evict her and hope for the best. You obviously can't continue this way.
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her threats to you may in and of themself may constitute a crime, and as a result you may be able to file charges... at the very least a paper trail of her issues will be an excellent defense to any future accustaion on her part.