Wrathia is the Keemstar of the SWT verse.
Diana knows she isn't guilty of murder, but is guilty of cheating and feels horrible about it, as well as the fact that she feels like she's living for the sake of the QB and CL who were "much better than her" and failing utterly at it. She also hates that she's in the unknown for why they died, and that there's no chance of redemption for her or the tragedy.
The people she spoke to: QB (Daniel), CL (Chelsea), Robin, Leo, the Vampires.

There's a data leak/spear phishing combo. Diana's not the only one targeted, but she's still a reasonable target. Funnily enough, there's nothing all that interesting in the Literal Vampire's texting, but it's very blatantly obvious that Diana cheated. It's unfortunate timing. It's double unfortunate if, say, she asked them to meet with her through text but then she had a physical alibi because she chickened out/had something come up (and there was no signs of collaboration?)

Diana had her boyfriend and the cheerleader both show up in her videos a couple times before they died.
Diana has a demon dad with connections that do actually work. And besides, she's innocent.
The killing of two kids (literally through poisoning and shooting, and then a failed bomb scare) was well investigated and shut down, even if no motive was determined. The person who did it was a new to the school outcast from a troubled home.
It's less about what the public thinks, and more that crackpot theories hit an already fragile mental state. She hasn't picked her major, she's insecure, the anniversary has come up, and what has she accomplished in three years? She could keep working hard...

...if she stopped isolating herself, if the Doctor hadn't died, if there wasn't a chance to correct Charlotte's wrongs even if she couldn't fix highschools.