This is what happens when everyone is stuck waiting for the next big update, all these crazy ideas and theories start flying around. I don't get why everyone thinks Bella has some dark secret when the only sketchy one, IMO, is Quinn with her drug dealing, that might lead to human trafficking of girls to pay off her debts.
Short answer? AL traumatized everyone to the point that they're expecting something crazy.
Long Answer: Because of the twist in AL about that character, everyone is expecting something like this from BADIK, that library scene with Bella kinda made a lot of players expect the worse. The mysteries surrounding her, that scene about asking for help, the closed door that even Jill doesn't know about, that talk with Jill in the bed... Anyway, unless Quinn kills Mona to shut her up next episode, Bella will continue being the suspect as the "dark twist" of the game. Honestly? I hope for something more realistic about her drama, even to be different from AL.
Isn't subverting expectations in vogue these days? That's the chance for DPC, make the door mystery be something silly and most people will be surprised.