Friend problem, Help.?

I have this friend. She's my best friend. She calls me all sorts of names, mean names. Today sitting in the living room she was talking to my mom, my sister and I we were talking about how the dog gained weight and then my friend said he's not the only one who's gained weight. We both looked at my sister and laughed and then my sister laughed too. But my friend then turned to me and said "I wasn't talking about her". I put on my pouty face and then she exclaimed "You look like a whale!" and started laughing. This isn't the only time she's said something about my weight. How I look or etc. Well after that I broke down and started crying so I walked out of the room. My mom didn't say anything. And my friend just said "Okay?" as I walked out of the room. I know that it was probably a joke. But I've finally been broken. I'm tired of it.