I still view Quinn as a prime suspect for the Cathy pic though, but I don't believe she will have conspired with the Jocks to do it if it was her doing. More likely I see it as Quinn unilaterally deciding to do it thinking that by getting the DIKs in trouble it would take some of the heat of the Jocks and she could try to persuade Dawe to make good on their previous deal.
Sounds like a terrible gamble. First of all, there's no evidence getting the DIKs in trouble will take some heat of the Jocks. Chad crossed a line without providing any kind of justification and Dawe isn't the perfect student either. They are perceived by teachers as potential bullies. Actions of others frats shouldn't change anything.
Secondly, Quinn intended to accept Tommy's offer. He provided her a safe and spacious place for their "private parties" and suggested her to involved more Diks as customers (Jaime, Leon and potentially the MC). Getting the Diks in trouble would definitely compromise everything. Her drug business requires several sources of profits. Sacrifice one for another isn't really smart. At this point Diks and Alphas should both be under surveillance.
Furthermore, time isn't on her side. Considering she has already been late with her suppliers, I doubt she has the luxury of waiting for the jocks to make good on their previous deal. Her attempt with the preps was a desperate move to get a lot of money quickly.
I still think Nick or Vinnie are more plausible suspects. Their potential motives are unclear but Vinnie is probably not mentioned so many times for no reason and Nick seems very uncomfortable with it. As a Dik, Nick has access to the vault and the laptop. Chad's blackmailer also sent personal pics of Arieth and the Diks. A selfie of a previous year including Rusty and Arieth and more recent pics (Jaime & Leon threesome during the cumpetition and Jakobs & Derek in janitor closet ). Which implied the blackmailer had access to Diks' old and new privates pictures. To me, a high scope plan to destroy the Diks sounds more interesting than a desesperate gamble.