Actually they can and do. Hypothetically lets say I get into a fight with someone but the guy doesn't want to press charges, if the police become involved I'm still getting charged with assault even if the guy says no. It's not up to the victim if charges are filed it's up to the police/prosecutor if charges are filed. This is why most schools have a police liaison officer, to make sure that stuff like that is dealt with in the proper way. However, "Game Logic"
Well, there's a keyword in there IF the police become involved. And well, they won't.
Cathy will not press charges and will refuse any legal action to be moved against the DIKs. It fits her personality to be like this.
But even if they become involved, it's her right to press charges or not. There's only not enough evidence and the college won't risk their image with an official investigation. It's just too unlogical, the police can't simple force themselves to investigate something they shouldn't be investigating.
Edit1: Of course it depends on the case in question. Assault as you gave as an example is another level compared to a naked picture.