Hermione Granger asked me to tell Sirius a lie about why she's avoiding us. The easiest way to do that, I think, is to make him think that she prefers the company of Slytherins. His prejudice is so strong that I'm positive that will work. All I'm asking from you- and anyone else you may choose to bring into this- is that if Sirius asks, tell him that Hermione spent hours of time in the Slytherin Common Room. She's given permission to add any details, even if they paint her in a bad light.