Yeah, bang the virgin daughter of the most famous supermodel is a thing. But... she's a bullied girl, she's a nobody for everyone. And to become a legend, and not a school legend, but a Hillside legend, you have to break the bank !
The ultimate price is obviously Charlotte ! The "nobody could get her" is not about the virgin daughter but the hot mother that nobody in the industry got in years ! I think Zak, a spoiled brat with a lot of money, has hired Johno to take pics... of Emma, Charlotte, Suzi, whatever that gives him a leverage to blackmail Charlotte. It happens to be pics of Emma. By scaring the mother enough, he probably hopes to make a dark deal with her : "open your legs, or I make her live hell... maybe I'll fuck her, take pics, then throw her away like a shit and post everything on the school's wall if you resist". That kind of shit.
And Johno is just greedy. He hope to have his share of the loot. Took pics, send them to the client and now tries to blackmail the sister and confuses her enough to bang her (or make money as it was a given option), knowing she won't tell anyone. Low risks and good price ? I think that's where he's involved.
Or maybe that's total bullshit but, hey, that's a plan