Infinite Magic by Linsey Hall

Things aren’t looking great for Cass Clereaux. For one, her greatest fear has come true. She’s stuck in the Prison for Magical Miscreants while her nemesis, Victor Orriodor, is out in the world, putting the last pieces of his plan into place. He’s wreaking havoc, all while she’s stuck in a stone box, awaiting likely execution.

Fortunately, Cass has just discovered that she’s the most powerful Magica in the world. She may have no control over her massive new power, but that won’t stop her from using it to break out of the world’s strongest supernatural prison. As for how she’s going to stop Victor when she gets out? She has no idea.

To have any hope at success, Cass will have to learn to control her magic and figure out exactly what he’s trying to accomplish. She’s going to need all the help she can get if she wants to survive, much less save the world. Luckily for her, she’s got Aidan Merrick and her sisters at her back, along with her allies in the League of FireSouls.