Well she has denied that they had sex, so unless they can force her to change her story what kind of testimony does the prosecution expect to compel her to give?
It also seems to me that there could be a breach of the 5th Amendment here since she already gave the police one story. If she says what they want her to say will she be testifying against herself for a "lying to the police" type of crime?
I'm not a lawyer, but I don't see the sense in forcing someone to testify when they are the alleged victim. Tricky terrain with her being a minor, but I'm not sure it's a precedent worth persuing.
It's the Mike Nifong system of finding witesses. "You have given our suspect an alibi. Is there anything about your story you would like to change before we throw you in jail on a trumped-up charge?"