As I see it, she decided to leave without revenge for the sake of the child, particularly after she discovered it was a little girl. She didn't want yet another little girl to grow up without her mother, the way she did. That said, it is depressing that the only way she thought she could give the child a chance at a real life was to walk away and leave her girlfriend and her stolen money to try to live a "normal" life with her new husband. Bleak, but interesting.