Realistic fiction, set in a high school, girl gets jealous of her best friends new friend who also gets the lead role

This was a fiction book I read in middle school, and the musical they were doing was Wicked. The girl ended up getting to be the understudy of her best friends new friend. If I remember right, the best friend met this girl at tennis lessons. I believe the new friends name possible starting with O. At the end, O ends up ditching her musical to go see a concert and the first girl does so good that her director says he’ll never replace her. Don’t know why, but it’s been bugging me to find out what this book is!!!

There was also a super specific line where the O girl says she’s “dabbled in musicals” before

Pretenders?

YES! Thank you so much I never would have guessed