BPD can't be used as an insanity plea since it's a personality disorder. It's damn near impossible to prove insanity in a truly mentally ill defendant. I think that it is a good point to raise to spare her the death penalty but it doesn't excuse what she did. She knew right from wrong when she was planning to murder him.
My ex (pending) has been diagnosed w/bpd twice in the past and even recently by a marriage counsoler. Reading this shit is beginning to make a tad nervous. Your descriptions are classic (as far as his personality). He used to say if I leave he'll just blow his head off. Now he hid his gun from me (I'm not the kookoo here!) And I'm wondering if he's thinkin about taking us both out at the same time.