If this is a shakedown, makes me wonder how many times this was done. The routine is pretty standard with regards to the investigation.
If she came with bruises from some other attack, those can easily be used with consentual sex to build a case of "rape".
Even with a proper investigation path, it comes down to was the sex consentual?
If she came to the event with bruises and that police/rape investigation indicates those bruises as having been aquired at the party the she is done. It also becomes an issue as to the natural progression of the bruises.
Remember the players are not putting up a consenual sex defense, they are saying they didn't have sex with her at all and that any bruises she had were on her prior to her arrival. It is possible that she had sex with someone else prior to the party, but thanks to DNA we can determine whose semen if any was left inside her.