Spookys reply is most aligned with my thoughts/opinion in this. Hypothetically speaking she may be suffering a personality disorder, (eg psychopathy, narcissist personality disorder). It may be wise to educate one’s self on these areas as it may give you a model to understand and explain her behaviour. In my experience this is/was key to understating, coping and eventually recovering from one bat shit crazy woman I dated years ago. Knowledge is power.
The solution, is to completely remove yourself from the situation. Find alternative work (appreciate it may not be easy) and whatever you do, do not confront her about it, as she will deny, blame shift, and not take any responsibility at all. Confronting her will add fuel to the fire and make you feel even worse than you already do.
I wish you all the best.