Well, my hypothesis (in addition to what we saw the night before) is also based on the (entirely personal) conjecture that Julia, before rushing to Sam's room, nonetheless asked Amber what had happened to her favorite hoodie (as we also saw with Sophia, in AWAM, it's the mothers who have to take care of washing their kids' dirty laundry and therefore they - and only they - have free access to their rooms). Therefore, since her mother knows nothing about it (and since I don't want to believe that Neil may have some reason to take her hoodie), the only one responsible for the "desperate" Julia should be her brother regardless of whether he has ever done anything like this before. What I think should piss Julia off the most is not so much whether she thinks her brother took her hoodie or not, but the certainty that he entered her room when she was not there.