This is making me feel really sad?

I really want to get this out of my mind, it's just bringing me down. I've known for a few years now that my grandparents aren't perfect, but I didn't see this coming. My grandmother from my mom's side has a problem. It hurts to admit this, but I think she is racist. I'm a 14 year old girl, my dad's side of the family is Italian and my mother's is Brazilian. My grandmother used to make fun of me last year because I was dating a black guy. I thought that I was making too much of a big deal out of it, so I ignored it. But what she said today really disappointed me. My uncle is in jail for not paying child support to his two kids (one of them is a 17 year old girl and a 15 year old boy). But it's not that he doesn't have the money, it's because he just doesn't want to pay (it's pretty obvious). But my grandmother called my cousin, and asked her if she could talk to her mom about dropping charges. My cousin told her that he deserves it, and that she should stay out of it. My grandmother hung up on her and started cussing saying "she is such a ***** a$$ (insert N word here)". I didn't know what to do so I just walked away. I haven't told anybody what she said, but it's really bringing me down. I mean, that's her granddaughter, how could she say something like that? I'm embarrassed by my grandmother saying this. She has never called me anything like that, and when I point out to her that I'm mixed she says "You don't understand, it's different. Don't worry about it.". And I just don't understand. I know she loves me, but why should she treat my cousin any different just because of her color? I just feel really bad right now, and I don't know how to get myself to feel better. How do I get this out of my mind?