My 9 year old has inflamed nipples after going to the beach, why?

After spending a few hours at the beach in the water, we go home. My 9 year old shows us her chest which is a normal flat kid chest, she hasn't developed breasts yet. Anyway her nipples are inflamed and red, and there are little red dots around them. Any idea what could've caused this? At first I thought it was sea lice, but I was with her the whole time in the water and there were no other red spots anywhere else except for both her nipples.