Cage of Deceit by Jennifer Anne Davis

Sixteen-year-old Allyssa appears to be the ideal princess of Emperion–she’s beautiful, elegant, and refined. She spends her days locked in a suffocating cage, otherwise known as the royal court. But at night, Allyssa uses her secret persona–that of a vigilante–to hunt down criminals and help her people firsthand.
Unfortunately, her nightly escapades will have to wait because the citizens of Emperion may need saving from something much bigger than common criminals. War is encroaching on their country and in order to protect her people, Allyssa may have to sacrifice her heart. Forced to entertain an alliance through marriage with a handsome prince from a neighboring kingdom, she finds herself feeling even more stifled than before. Now the cage Allyssa so longed to break free from might just be the one thing she has to fight to keep intact.