First when the Gemara wants to bring a Rayah that when the Gemara says that the Money goes to the father, the Gemara says maybe that is only talking about by a ketanah who has no yad in kiddushin but a naarah who has a yad maybe she collects the money! So the Gemara says No, because of the Pasuk of Bineureha Bais Aviha all the profits of the naar goes to the father. Then the Gemara wants to know From where do we know maaseh Habas l'av? so they bring a pasuk vchi yimkor ish es bitoi l'ama---- Mah amah maaseh yadeha l'rabbah af bas maaseh yadeha l'aviha. The Question then is, why not learn it out from bineureha bais Aviha? The Gemara says No, because that pasuk is talking about nullifying vows.
My question is why before was the Gemara able to use that pasuk as a rayah to something other than nullifying vows?
Yochanan Gordon, Lawrence New York U.S
You missed an all important word in the Gemara: "Ela." The reason the Gemara brings the Limud of Ma'aseh Yedei ha'Bas is to refute the possibility of learning Kesef Kiddushin from Bin'ureha.
The outline of the Gemara is thus as follows: The Gemara wants to learn that Kesef Kidushin goes to the father from Bin'ureha. The Gemarah counters that if we can derive that money of Kidushin goes to the father from Bin'ureha, why did we need to learn Ma'aseh Yedei ha'Bas goes to the father from l'Ama? We could have learned that too from Bin'ureha. "Elah," Bin'ureha only applies to Nedarim, and therefore we cannot learn neither Ma'aseh Yedei ha'Bas nor Kesef Kidushin from that verse.