The Counterfeit Lady by Alina K. Field

Freedom!
Vowing she’ll never submit to an arranged marriage, an earl’s daughter bolts for the remote seaside cottage that should be hers upon marriage.
But instead of a quiet respite from her controlling family, she finds her refuge occupied by the last man she ever wants to see again—an American artist, who’s also a thief.
And quite possibly one of her father’s spies.