Captive of the Pirate King by Rebecca F. Kenney

Veronica wants nothing more than to find her brother, who sailed away years ago. But when Veronica’s ship is captured by pirates, she’s determined to save her own skin, while keeping her magic and her gender a secret. Disguised as male, she finagles a spot as a cabin boy aboard the buccaneers’ vessel–which is bound for Ravensbeck, a stronghold where the Pirate King holds sway. He may have the answers Veronica seeks–but getting those answers could cost her more than she’s willing to pay.
[Trigger warnings: violence, reference to a past abusive relationship, murder, threat of rape, forced tattoo, brief mention of childhood sexual abuse]