I think, and this is just my opinion so take that for what it is, that it's important that you document all of the conversations you've had with her to this point. If it is in the past, write it down to your best recollection. Take those with you when you file your report.

You should know, however, in some jurisdictions in the US, an accusation of sexual assault requires either the victim stating "no" or being in a state where they are unable to consent. It sounds like you'll need to elaborate on your situation and you wouldn't be the first victim to report that you were unable to consent because of previous trauma, fatigue, intoxication, etc.

I add that because you will likely be asked what you did when she tried to force sex with you and they might not word it gently. Writing out the situation will help you prepare for this conversation. Hopefully, it will lessen the emotional weight of re-telling your story to a legal authority.

Also, please know that counseling may help in your situation. A mental health professional is unable to offer you any legal advisement re: whether or not you should report but they can offer you guidance throughout the process. Given your history of past abuse and recent assault, I hope you choose to seek professional supports right now.

Finally, if at all possible, have no further contact with the girl until you've spoken to someone about the legal obligations of your situation. You might expect things to get tense, at some point, so protect yourself in any way you see fit including (but not limited to) talking to the RA's and requesting a new dorm assignment ASAP.

There's no way of what's going on in her head right now. She could be seriously mentally ill or she could be a victim of trauma herself that doesn't understand sexual norms. She could just genuinely not understand that you meant "no" that night. I'm not making excuses for her but I'm offering you a preview of one of any number of justifications she might present to authorities to explain her side of events.

Remember... nothing she says changes how you feel about it right now and that's ok. You feel very harmed and you deserve to be supported for that by those around you. I'm so sorry you didn't get that support from family. Many people don't and, thankfully, that's one reason why professional supports like counselors exist. I see you getting very wrapped up in what others might think... Try, if you can, to just focus on what you think and what you need for the next few days.

Best of luck to you.