YA Book With Female MC Who Can Control Water

Trying to remember the name of this YA book/series I read a long time ago, about a girl named Candace (not sure of exact spelling) who can control water. I remember she goes to some kind of academy/program for training superheroes and that she had a brother (named Matti possibly?) in the program too who was like part of a popular superhero team or something. In later books I think her powers evolved to control blood in herself and maybe others?

Any help in figuring out the name of this book would be appreciated. I've tried searching the Internet extensively and no luck.