Kathryn didn't even start out chaste originally, she was having regular sex with Luke and, presumably, had boyfriends before him. But she wasn't ever "corrupted". And when a young woman is "blackmailed" (by threatening her favourite musician? Really, that's all it takes?) into sucking three cocks in the back of a trailer like some random groupie, then it's safe to say she has been corrupted.
So now, Luke's attempts to "corrupt" Kathryn are like pissing in the ocean: you ain't adding anything meaningful there, son.