Hi N.!
I'm sure that this is a difficult time for your daughter; especially in the girl's locker room at school and in the dressing rooms at stores. How I remember that time in my life. I was slow to develop in that way too and kids can be sooooooooooooooo very cruel.
My suggestion is if you have the awareness and faith in God, you can teach her that God created her, and regards her as very special, and very beautiful. Teach her that God has a wonderful plan for her life, and that pleasing God is a worthwhile endeavor. If you don't have that background, understanding or belief, you can learn together, and it will help both of you, and you can grow closer together. Pleasing people is impossible because, well, let's face it, people are fickle and you will always get conflicting messages. You won't get that from God. I didn't learn about my identity in Jesus Christ until I was in my 40's and it would have been invaluable when I was a child and teenager!!
I hope that helps you!
T. H.