firstly, let me say that what you and your Master did was very brave, and i can see that Y/your intentions were good. however, if this girl has suffered so long through abuse, its irresponsable to place her into a situation where she must once again submit to someone, who has the power to abuse her. to us, this is not considered abuse, but to someone who has lived with not being able to speak her mind, not being able to be her own person, and generally being used as a punching bag, then this is basically like her going from one abusive relationship, to another. do you understand what im saying? what she needs right now is counceling, someone who will be able to help her gain her self esteem back, and learn to live life on her own again. there has to be a transitioning period between the time she spent being abused, to getting into another relationshp, which she may in some way connect in her mind as being a safer form of the same relationship she found herself in previously. this may be totaly untrue for her, but im just going to throw this out there; maybe she feels as if this relationship is close enough to her old relationship for her to feel comfortable, but in some ways will allow her to experience freedoms, such as a safe word, that she did not have with her abuser.
the best thing you can do for this girl, is to help her find a good therapist, and help her get her life back together. neither you nor your Master are trained professionals, and as such are not able to properly help this girl in any way, shape or form while shes in the state that she is in. you may possibly keep her in your home for now, but in time help her find a place of her own, so she may be independant(which im sure she will fight, and fear, but later on she will thank you). im not saying for you to just dump her..but if you ever want to help her get better, then she must establish a healthy sense of self, independance, and a good self esteem before she is ready to join into any kind of relationship, or endure any sort of training. be her friend, but dont be her Dominent, or have her in a place where she believes she is stuck in the role of "submissive" or "slave".
best of luck!