She knew she would because Bruce loved her so its a no brainer that he would choose her over that Two-face douche.
Two-face was pissed because 1) he lost his love and he was horribly disfigured, i'd be pretty mad at the world too. 2) because that lady cop was supposed to be in charge of transporting Rachel to some place safe.
But instead she helps the bad guys get to her. Granted the lady cop said she didn't know they were going to hurt them, but what did she expect ya know?
And ewwww i know! She looked so old and frumpy, they should have gotten someone more Batman's speed.
But i guess they were trying to replace Katie Holmes so i guess Maggie Gyllenhaal was just as homley so it works out. =)