Before I tell you my long story. Don't assume anything, absorb information and be there for her, but don't make any actions on her behalf. Don't assume she's lying, but don't assume you have all of the information needed to make some kind of judgment. Offer help, let her know that what happened is Not okay, and again, offer to be there for her.

I once started dating a girl in a very similar situation. I met this girl through a chain of friends. She told me she had been raped several months prior and did not seem phased by it. It struck me as odd that it was seemingly so important that she would tell me so quickly in the relationship we had, but it wasn't important enough for her to explain her true feelings on the subject. It didn't seem important enough for her to call the cops.

Her and I stopped seeing each other soon after, we just didn't really have any chemistry.

I got in contact with the guy a couple weeks after her and I stopped talking, and confronted him about it even though it wasn't my place. He pulled out his cell phone and said that he has heard the same story from several other people, some of which called the police who also confronted him. On his phone he showed me texts that she had sent him, even while me and her were together, asking to get back together and saying that she would tell people he raped her after they had consensual sex and he chose to not be with her. Some of these texts were less than a couple hours old. His reason for not being with her was because he picked up on signs that she wasn't "mentally stable." Turns out, it was true. She later had a child and the child was taken from her custody after she was found to be unfit. This guy had to move away from his hometown because this girl had convinced so many people he was a rapist. When she originally told me this story, I was baffled as to why she didn't have the police involved. I pressed her for a week or two to take action while I offered my help.