Curling, you weren't there to see what happened, this is your fatherly instinct kicking in. Your daughter was probably humiliated because she was being busted in front of the whole world and may have projected this to you in a somewhat inflated story to take the emphasis off of her humiliation, the bad she did and to focus your attention somewhere else.
How perverted is a cop really going to get in front of a water park with (presumably) 100s of people watching? Sure, there's bad apples, but even if it happened like she said it did, he was likely checking for drugs.
Normally, these days, they will have females check females though. If you feel something happened (which will look ridiculous at court because you weren't even there), then your daughter should mention it in the file of a complaint (which she should be willing to do if it really happened) and suggest that female officers search females.