I did wonder what her get-away-plan could be there ;) Unless she simply planned to tell him that she'd changed her mind once she was sure the ship was empty? I've seen some fans claiming that she intended to wait until he passed out from how drunk he was, but he didn't seem drunk enough for that to me - he was walking fine, even carrying her at one point, and talking fine apart from mixing up letter in the Jolly Roger's name. She'd have needed to keep pouring him more drinks and I think that would make him suspicious - he'd probably assume she was planning to rob him.

I think, given her history of preferring one night stands at this point, she secretly wanted to use the opportunity to sleep with a version of Killian without the complication of him being in love with her or the pressures of a relationship.