No girl can like to be violently raped.
If she re-enacted the same situation is for the reasons that tinyrabbit explained very well.
No one ever wants to be raped unless he/she has serious psyche damages.
This is not the case of your girlfriend.

One question: has she really got over it? Has she seen it thru with a therapist and now she's fine about it? If not I guess she should. Your adding that she had voluntarily sex with her rapist seems like she has not put in perspective yet what happened to her.
If she starts any therapy, you might want to join her, at a certain point, to discuss this specific part together with her therapist.

But you should be honest with your T expressing the way you feel. There is nothing wrong with our emotions. We must learn to read them correctly and act after them in the proper way.
If you keep hiding them you are not helping yourself in stepping forward.