Should i believe my girlfriend when she says she got d?

going off of her memory and what she tells me: In june of 2008 when my girlfriend was a freshmen in high school, while having a party at her house she was blackout drunk and went into her room to p out, and shortly after 2 guys came into her room and took advantage of her. she only remembers bits and pieces of it, she only remembers vividly one of the guys (both were 2 grades above her) having with her and one of the guys violating her in another way, although at school the following week the 2 guys told everyone they "ran train on her". I have talked to other people and her friends, many do not know what happened. one friend claims she brought one of the guys (or both) into her room with her, although she persist she went to p out by herself before anything happened. She is very distraught by this, but i find it uncomfortable knowing she hardly remembers that night or specifics of what happened, especially since it was at her own house that many of her friends were at. also her brother and mother doubt that it was that happened that night, although her father reported it to the police when she told him. (we started dating in march 2009 and i told her to report it in november 2009, the case hasnt gone far yet). furthermore, i know she had 4 ual partners before then, and was promiscuous and kissed about 15-20 others before june 2008. i know she was a slut back then and could have blacked out and not known what had happened, but she truly thinks it was even tho she doesnt remember. what do i believe?