I didn't see or hear anything that hinted she was bi-polar, must have missed that. What I did hear and see is that she had Delusional Disorder.

The definition for DD would be right on if this is what they are portraying her to have:

Delusional disorder, previously called paranoid disorder, is a type of serious mental illness called a "psychosis" in which a person cannot tell what is real from what is imagined. The main feature of this disorder is the presence of delusions, which are unshakable beliefs in something untrue.

http://www.webmd.com/schizophrenia/delusional-disorder

BTW, I agree about the ending. It made my jaw drop to the ground. But, in the same breath we had a case similar here in Illinois where a woman did what she was about to do. I wont say since some may not have seen the episode.