Some people are VERY stupid about what they put on Facebook. You never know what she might have on there. If she's been dating...she might have comments on her wall or even added "in a relationship" on her page. Yeah...I've actually heard of people doing that before the divorce is final.
The ex-husband of one of my co-workers did that. He ended up marrying the woman that he cheated on his wife with. He was even stupid enough to put on his profile when their anniversary was. Guess what...it happened to be when he was still married to his first wife.
I don't know what she was able to accomplish with the information though.