I was going to say probably an ingrown hair. but around her nipples. she needs to go to the doctor.
Is it possible that she has chicken pox? It usually starts on the trunk of the body - chest area. They look like pimples and itch - don't pinch them or scratch if you can help it.
She might find a bath with baking soda will stop some of the itch.
These pimples could be from scabies, bacteria or fungal problem.
It is not normal for a child of 10 to get pimples in the armpits and around the nipples.
Do you think it possible that she may have used an underarm deodorant and has an allergy to it?
I would take her to see her doctor to get her checked out.
Best wishes.