I'm not so sure
To clear things out:
MC was framed by some person, that gave Chad some text or photos which points to his relationship with Troy and that they are gays. In the way that MC knows about them and want to blackmail Chad somehow with this. If that was the Sarah (or Melanie), I wonder why. If it was someone else, I wonder how it's still not spreaded among the campus.
The whole idea was to provoke Chad, which worked out, but what did they want to achieve with it? Whoever it was? So that he beats up the MC and then MC runs away from college? Or someone knew in advance about the consequences and potential complaint against Chad and that this would lead to his resignation as president of the frat (at least). In this case, the version with Sarah and Melanie looks illogical, because they looks like to be friends. But knowing the bitching and mean nature of them I won't wonder a lot in such case.
Besides that picture about Chad's orientation, there were many pictures of Arieth's infidelity that should have sparked a new war between DIKs and Jocks. The same episode shows that the fraternities are constantly feuding over girls and these pictures were supposed to provoke a war again.
But probably Chad decided to attack MC first and disrupted the plans. He was suspended and the war didn't happen because of that. And the attackers had to adjust their plans. And already in the 4th episode there was a direct hit on DIKs themselves.
And what do we have in the end?
The jocks lost their influence.
DIKs lost influence.
And who gained influence? The dorm girls. It was their party in ep8 that drew a lot of people because DIKs didn't have parties. And no one goes to jock parties except the jocks.
In favor of this theory is the fact that posters with DIKs appeared after the Halloween party when it became clear that DIKs returns and becomes the center of attention again.
There's a lot of reasons why the dorm girls decided to do this.
1) Revenge. Rusty and Tommy get laid a lot, a large number of girls came out of the mansion to a DIKs song. Probably some of the girls were really into Tommy or Rusty. Some of them just hate DIKs. For example, we know Becky is friends with feminists. And as we see DIKs and Jocks often feud and bully them.
2) Their own sorority. The girls in the dorm probably want to start their own sorority. But maybe the college either doesn't have room or there's a limit on student organizations or some other reason and in order to create one they need to destroy or at least weaken one of the fraternities. In fact, I think there's going to be a strike against HOTs soon.