Yevamot, Chapter Thirteen, Mishnah Two
This mishnah provides three statements as to which type of minor girl can be married off by her brother or mother and before reaching majority age make a declaration of refusal.
Which minor must make the declaration of refusal?
1) Any whose mother or brothers have given her in marriage with her consent.
a) If they gave her in marriage without her consent she need not make any declaration of refusal.
2) Rabbi Hanina ben Antigonus says: Any child who is unable to take care of her token of betrothal need not make any declaration of refusal.
3) Rabbi Eliezer says: The act of a minor has no validity at all, rather [she is to be regarded] as one seduced. The daughter of an Israelite [who was married] to a priest may not eat terumah, and the daughter of a priest [who was married] to an Israelite may eat terumah.
Section one: When the mother or brothers marry off the girl she must consent to the marriage. If she does, she may later on make a declaration of refusal and thereby annul the marriage. However, if she does not consent, she need not even make a declaration of refusal.
Section two: R. Hanina adds in another criterion for which type of girl must make a declaration of refusal in order to leave her marriage. If she was married off by her mother or brother at an age when she couldnt even take care of her token of betrothal (either money or a document), then the marriage is totally invalid. According to the Rambam, a girl under six by definition cannot take care of her token of betrothal and a girl over ten can. Girls between six and ten are checked to see if they have this capability. If they do not, then they do not need to perform meun.
Section three: According to R. Eliezer, even if her brother or mother married her off, she is not considered fully married, rather she has the status of one who has been seduced. This is a way of stating that there is no validity to the marriage and therefore if she is the daughter of an Israelite married to a priest, she does not gain the right to eat terumah and if she is the daughter of a priest married to an Israelite she does not lose the right to eat terumah. According to the Talmud, although she is not at all married to him, R. Eliezer still requires her to make a declaration of meun to leave the marriage.