What do I do in this situation?

I was at a school picnic and one of my friends (she's a girl) was sitting away from everyone else and I went to see what the problem is. I got close and turns out, her dad was speaking sternly to her telling her how big her belly was compared to everyone else. She was crying the whole time. He went on for five minutes about how much bigger she was than everyone else. It is true that she is quite large (all of her weight is in her stomach), but I don't know what to do. This girl is a close friend, not a girlfriend.