don't go near the water chapter 1

Elsa was a normal 16 year old. Except for one thing. Her mom didn't let her or her brother swim. But one day when Elsa's friends pressure her to swim, it feels natural. like she's been in water her whole life. but on one of the laps her legs start hurting and she can't move. after that she starts having weird dreams and is able to manipulate water. what's going on with her?