Actually had a idea for something like this, but the protagonist was the 6 year old, and was freed after 10 years. Then she was recruited by a agency to find the people that murdered her parents and framed her.
Heart Beat Audio - Reddit Writing Prompt: Magic is Hereditary Part 1 Me and my co-host are not the authors of this tale. All rights of the story go to the reddit user reostra. Link to the story https://www.reddit.com/r/WritingPrompts/comments/4gvu9w/magic_is_hereditary_but_the_childs_powers_is_the/d2l6nfs