What should I tell my mother?

I have this “friend” let’s call her Sam. Sam used to be my best friend until last year. She was really rude to me so I stop talking to her. This has happened before but my mom and her mom are really good friends so we “got back together.” Well Sam is perfect in my moms eyes so my mom always compares me to her. This really hurts because I am her own daughter and she treats me like dirt. I still see sam once a week because we have a dance class with her. I don’t know what to do, I am heart broken? What should I tell my mom?