In A Midsummer's Night Dream, Theseus tells Hermia that she needs to obey her father, because in that time in Athens, daughters were the property of their fathers until they married, and then they became the property of their husbands. It was the law of Athens that she must obey Egeus.
Theseus also points out that Demetrius is a fine choice for husband, as he is well-bred, well respected, and was her father's choice for her. She, however, counters that she does not love Demetrius and as a young girl she wants to marry for love, not money.
Theseus did, however, give her some options. If she chose to disobey her father and the law of the land, she could join a convent and shun men the rest of her life, be banished from her homeland forever, or be put to death. None of these options are particularly good ones, so she had strong motivation to "make the right choice."