D..
I don't have daughters, but I will tell you that my breasts hurt when I started developing. I specifically remember my dad praying at night with us for nightly prayers and asking God to help my breast pain, LOL!
That was 4th grade. I got my first bra in 5th grade. I don't remember when they stopped hurting, but I was thin and small-breasted. There was a skinny little girl named Marsha in my 5th grade class who just had little buds. You could see the little buds through her shirt, but she had no breasts at all. The boys teased her because she wasn't wearing a bra. It would make her cry. Her mom wouldn't buy her one because she didn't have breasts yet. FINALLY, in the middle of the year, she got one. I suspect that the teacher had a talk with the mom because Marsha was in tears every other day, and finally had the courage to tell the teacher. (I wonder why we girls didn't go tell on the boys - I knew they were teasing her, and I didn't think to tell the teacher either!!!)
So I guess I would go get her a bra when she asks for one.
I hope that the pain goes away soon. Perhaps wearing a sports type bra might help with the pain - I don't know.
Dawn