She was raped, plain and simple. She couldn't give consent.
At a bare minimum, she needs to go to the hospital or a clinic ASAP and get checked out. She could have been exposed to an STD and/or become pregnant. She also needs to write down what she does recall, while it is fresh in her mind.
I'm wondering if someone slipped something in her drink at the party? They may be able to do some tests at the hospital, depending on how much time has passed.
What kind of sicko takes advantage of a girl who's semi-conscious??
Was she already wasted when her "girlfriend" left? If so, you have to wonder what kind of "friend" this girl is, to leave her alone in that situation.