This girl talked about my recently dead mom?

Everyone seems to have whispered it around me as usual. My dad told the school that I needed time because she had cancer, then they, as the old lonely b****es they are, snooped into it. They assumed and got it right, she died that same night. Then they gave me so much pity that it went around the school about how I got seriously depressed for the first time. Months later, Belinda(a gossip girl of the school, knows every rumor that goes around) is joking and stuff as my best friend locked my backpack. Belinda goes,"Dude, do you have a dead body in your bag?" I joke around saying,"Yeah." and she says,"Who is it, your mom?" I wasn't sure if I heard correctly, but when Shelby(best friend) took the bag from her and said,"Thats f***ed up.", I knew I heard right. When I asked at the time what Belinda said, Shelby told me it was nothing. Shelby seems to think I'm clueless about it, which I thank her for, I hate pity. I don't know how to handle this situation, I was taught by my dead mother to put some sense into people no matter what their sex was. I never actually took the advice, but right now, I feel the need to, at least with this ugly chick!