On a Biblical level, a father can arrange a marriage for his daughter when she is a minor, and this is considered a full marriage according to the halakha. In the event that there is no father, the Sages instituted a Rabbinic marriage that can be arranged by the girl’s mother or older brother. This was done in order to protect her interest in a society where a young girl with no father may be taken advantage of. Even so, such a marriage is not a complete one. The girl has the right of mi’un – refusal. At any point she can announce that she does not want to participate in this relationship and the marriage will immediately become annulled, as if she had not been married at all.
The Mishna on our daf teaches that the possibility of a Rabbinic marriage exists only if the mother and/or brother informs the girl of what is going on. If they do not tell her that a marriage is being arranged for her, there is no need for mi’un at all. The Talmud Yerushalmi illustrates this as follows: If they dress up the girl in a fancy dress and tell her that she is to be married to a particular man, that is considered informing her. If they dress her up but do not clearly tell her that at the party she is to be married to him, that is not considered informing her. Some argue that this will be dependent on the age of the girl and her awareness of the significance of what is going on around her. Thus, a girl who does not yet grasp the significance of marriage will not even need to refuse the marriage.