I think anger can be a good thing! I know anger is unwanted by many, but I see it as an emotion that can spurn a lot of change. I don't know if I would focus on getting rid of the anger. I think perhaps it's best to examine why you feel this way. In your case the anger comes from the fact that this perpetrator hurt someone you love very much. I assure you that your feelings of anger are quite natural and to be expected.
When she is upset and comes to you, I understand why you are trying to calm her down. However, you are now a part of this equation and your feelings are quite valid. I urge you to find a way to deal with your feelings outside of her. Maybe this involves stepping away during those moments. She may get upset if you do this, however your job isn't to be a therapist and listen to everything she has to say. Maybe this sounds hurtful, but if there are things that she says that push you to the edge, then it seems that boundaries are needed. Is she in therapy? If not, I urge her to go and find a therapist. Again, it's not your job to fix her. You are a human and you have your limitations (just as we all do). I think that healthy separation is needed and she also needs to work on finding outside support. A partner is not meant to be a surrogate therapist.