It seems reasonable to assume this actually happened as described (photographic evidence), so to Wyler's point of "why didn't she report it?'
Although 2001 seems recent to most of us, a lot has happened around the perception of professional conduct and sexual harassment in those 17 years. It is likely that having been treated in such a manner, this individual had little or no faith in the "chain of command". Allegedly, she has been sexually assaulted and abused by a large group of male servicemen, some of who were in positions of responsibility, but yet participated or condoned in the assault. It is not difficult to imagine a young isolated female would not choose to report this to the very people who were responsible.
If nothing else, the whole sordid tale of Operation Yewtree demonstrated time after time that young impressionable people are easily intimidated by those in authority and will choose not report crimes until years later . You can argue all day whether 21 is "young and impressionable" but if placed in a situation several thousand miles from stability and safety, after being assaulted by multiple assailants you can understand whether reporting it is the obvious thing to do. I like to think we live in slightly more enlightened times these days, but this was very real event back in 2001 and the time it has taken for her to report it has no bearing on the facts of the case. We should all hope this type of behavior is consigned to the history books while ensuring those guilty of it are held fully accountable.