What was the motive? (SPOILER)

I enjoyed the movie despite some obvious plot holes, but during the ending I was really hoping that Ann Marei would survive! Not that I liked the character, I just wanted to know "Why?"... In the very end she says something about "I can't live broke", but I can't recall that the movie ever portrayed her and her husband as being particularly broke? I'd like to think that it would require some sort of desperate need for money - something like owing the mob money - in order to transform the sweet girl we see (or that we're meant to believe anyway) in the beginning into the cold calculating killer we see in the end... that's my biggest problem with this movie - Ann Mareis motive is reduced to "I can't live broke"... that's just to vague for me, I would have needed some more background story and character development.