The Assassin's Daughter

Lenna has been hiding from the Guild since she was born.

If they knew about her magic her life would be forfeit. 

She must brave the possibility of discovery by entering the Guild under the guise of a human recruit after her father goes missing. 

She realizes she's bitten off more than she can chew when she sees her new instructor is the same guy she met a few months before. 

It doesn't seem like Cade recognizes her without her disguise, but if he does and blows the whistle, she's as good as dead and so is Papa.