What Causes Nipples Pain?

Okay. My daughter has been swimming in a lake for a few weekends in a row. She came to me yesterday, and told me her nipples have been hurting. Well When I looked they were completely rubbed dry, i guess you can say, then you can tell inside the bathing suit where it was like bleeding. Her nipples are really small, and kinda like not even there. What's wrong with her?