The first thing that came to my mind when hearing about this was that she may have a severe manifestation of a personality disorder. She planned it unbelievably well, so I believe she is fully sane. Someone with a personality disorder is not at all necessarily legally, "insane".
She also seems to be a tad bit obsessive. Well, more like over the top of a mountain in that area. And, since this was planned better than any murder mystery writer of fiction could probably ever imagine, buzz's theory may be correct.
I am very glad that she was caught before she could commit murder. She is very dangerous, and I hope she receives a long prison term for the safety of whoever gets in her way.
Lion