Plot stupid as fuck. Girl just tell him who you are and get revenge then. Gonna be one of ...

She doesn't gain anything right now, by telling him who she is (as she still doesn't have the means to impose her side on anything at this moment). Worse even, if the dude turned out to be someone horrible like her stepfather, he could choose to lock her up and beat her till he gets her to agree to be the one to ask for divorce, so she can forfeit all her inheritance to him.