Am I a bad friend?

Hello, I really hate to make this post, because this is about someone who is known/I've always considered my "best friend." Recently, I've been struggling with my weight a lot. I've lost a ton of weight (30 or so pounds) and I've been struggling with keeping it that way. I've confided in said friend and told her about my struggles. She is around 119 pounds, and has always been extremely thin. Whenever me and my other friend (who also struggles with weight) is around, my 'bsf' talks about how fat she looks, or how fat she is when in reality she is one million times skinnier than both me and my other friend!! I understand that even skinny people can be insecure, but she basically begs us to call her skinny. It's most definitely just insecurity she has, but it's extremely frustrating when she's aware that my friend and I are struggling while she's never been above the 120's. I'll also add, she only acts like this at school. When it's just me and her , she's completely normal. She also has been acting stupid and asking basic questions (ex: "Hey, what's my favorite color?" or "Hey, what's my address?") while I'm trying to do my work!! Am I an asshole for finding this frustrating? I've felt recently just like a terrible friend for getting mad at her but I genuinely can't control it. I feel like she's suffocating me, but I don't want to loose her because I love her still. Help? Anyone?