Yevamot 107 - Underage wife
Beit Shammai says that she can refuse the marriage only after engagement but not after the marriage is complete with the chuppah. Had refusal been allowed when they are already living together, people might make a mistake and say that marriage with an adult woman can be dissolved without a divorce (Get), perhaps if the marriage conditions were not fulfilled. However, Beit Hillel allows her to refuse anytime: people know that a marriage of a minor girl is unique and can be dissolved without a Get.
Another type of logic: Beit Shammai says that if the girl can walk away, the man will not prepare the wedding reception, with all associated expenses, just to see it go to waste. However, Beit Hillel allows her to refuse any time: both the man and the woman want their wedding to be known, so the man will not hesitate to throw a feast to get married.
Art: Wedding Dinner by Jacob Gerritsz by Van Hasselt
