Gemara

44b (Shmuel (and Rav)): If a minor accepted Kidushin without her father's knowledge, she needs a Get (lest her father consented to the Kidushin).

(Ula): She does not need a Get.

45a (Ravina): Even those concerned lest a man consented to his daughter's Kidushin, are not concerned lest a man consented to his father's Kidushin.

Question: Perhaps the son told the father that he wanted to be Mekadesh her!

Answer (Rabah bar Simi): Really, Rav and Shmuel would be concerned. Ravina explicitly said that he does not hold like Rav and Shmuel.

45b (Rav): If David agreed to his daughter's Kidushin (to a Kohen), and went abroad, and she had Nisu'in, she may eat Terumah. If David returns and protests, she must stop eating.

(Rav Asi): She may not eat, lest David return and protest, for then retroactively, she was forbidden to eat!

A case occurred, and Rav was stringent, like Rav Asi's opinion.

46a (Rav): If a minor became Mekudeshes without her father's knowledge, she can cancel the Kidushin (herself), and also her father can.

(Rav Asi): Her father can cancel the Kidushin (himself), but she cannot.

Question (Rav Huna - Beraisa): If Levi seduced Leah to have Bi'ah, her father, or even she, can veto (the Kidushin). We learn from "Im Ma'en Yima'en."

Answer (Rav, on behalf of Rav Asi): Perhaps this refers to when the seducer did not intend to be Mekadesh her through Bi'ah.

Rishonim

Rif and Rosh (2:7): Rav and Shmuel say that if a minor accepted Kidushin without her father's knowledge, she needs a Get.

Ran (18b DH Itmar Ketanah): His consent works even after the money was given because every man wants and is commanded to marry off his daughter. Zachin l'Adam she'Lo Befanav (we may do something beneficial for someone in his absence). There is a negative side, that she leaves his Reshus, therefore it works only if he consents when he hears.

Rif and Rosh (ibid.): The Halachah does not follow Rav and Shmuel, for Ravina disagrees. He is Basra. Even if her father consented, it is not Kidushin. If he agreed to her Kidushin and went abroad, and she had Nisu'in, she may not eat Terumah. Since Rav was stringent like Rav Asi, we follow Rav Asi.

Question: Why did the Rif bring the argument of Rav and Rav Asi regarding Nisu'in without his Da'as? The Rif holds that consent afterwards does not help!

Answer (Rosh and Ran 19b DH Garsinan Tu): Nisu'in is different. Since he consented to the Kidushin, it is as if he told her to have Nisu'in.

Ran (ibid.): Rav says that if a minor became Mekudeshes without her father's knowledge, she can veto the Kidushin herself. Since he did not consent at the time of Kidushin, she can retract before he consents, and his consent later will not help. Since the Kidushin did not take effect yet, she can retract her acceptance l'Shem Kidushin. The Halachah follows Rav (regarding veto). This is relevant even for us (who rule like Ravina), even if he explicitly consented after her veto. However, if she or her father did not protest, she is Mekudeshes from when she received Kidushin, even if the money was consumed before he consented. Rav established the Beraisa to discuss seduction not l'Shem Kidushin. Surely, it was not in front of her father! Nevertheless, if he consented, the Bi'ah would make Kidushin, even though there is no remnant of the Bi'ah when he consents. This is like Rashi; if her father consented, she is Mekudeshes. Kidushin and Nisu'in are possible without his knowledge, and her veto is relevant. Perhaps the Rif agrees that immediate consent makes Kidushin. He just says that if he consented later, we are not concerned lest he consented initially. The Rambam holds like this.

Rambam (Hilchos Ishus 3:13): If a girl before Bagrus accepted Kidushin from Levi without her father's knowledge, she is not Mekudeshes, even if her father consented afterwards. She or her father can protest, whether she became Mekudeshes in front of him or in his absence.

Question (Ran, ibid.): Since the Rambam holds that she is Mekudeshes only if he consented immediately, in what case is her protest relevant?

Answer #1 (Maharik 32:1, cited in Beis Yosef EH 37 DH u'Maharik): If her father was present at the time of Kidushin and did not protest, we assume that he agreed, and she is Mekudeshes. Since her father was not Mekadesh her, the Kidushin depends on her and she can veto it later.

Answer #2 (Beis Shmuel 20, citing Bach DH u'Mah she'Chosav sheha'Rosh): If the father consents afterwards, Levi can be Mekadesh her now through her initial acceptance, unless she protests.

Rosh (2:6): If a father consented, the Kidushin works retroactively. It is as if he told her 'go receive your Kidushin.'

Poskim

Shulchan Aruch (EH 37:11): If a minor or Na'arah accepted Kidushin without her father's knowledge or had Nisu'in, this is nothing, even if he explicitly consented later. Some say that if he consented when he heard, she is Mekudeshes from then. If he was silent and later consented, this shows that he consented when he heard. She is Mekudeshes from then, even if the money was already consumed.

Chelkas Mechokek (19): The Ramah says that the Kidushin takes effect through the Hana'ah the father had that his will was done.

Beis Shmuel (18): The Ran and Rosh say that the Kidushin works due to Zechiyah or Tze'i v'Kabli. It is retroactive, even if the money was consumed. Why does the Shulchan Aruch bring only the opinion of the Ramah, that it is from when he heard? Perhaps it is because a Shali'ach Kabalah must be appointed in front of witnesses, and his consent (i.e. hearing about the Kidushin) was in front of witnesses.

Shulchan Aruch (ibid.): If she or her father protested before he consented, she is not Mekudeshes even if he consented later.

Rema: Some say that if the money was consumed before he heard, she is not Mekudeshes.

Source (Mordechai 513): The Rif holds that consented of the father does not help. Avi ha'Ezri disagrees. Perhaps the Rif discusses when the money was already consumed. Others (Ra'avan and Rashbam) also say so.

Gra (33): The Mordechai learns from a girl who did Mi'un after maturing. Bi'os before maturity are not Mekadesh her now.

Rema: Some say that if he was initially silent, it is as if he consented.

Beis Yosef (DH v'Chosav Od d'Heicha): The Mordechai says that if the father was initially silent, even if he protested later, it is as if he consented.

Beis Shmuel (21): All the Poskim disagree with the Mordechai.

Darchei Moshe (8): The Ramah and Rosh hold that silence is not like admission. The Rivash (193) brings both opinions. He also says that once the father protested, consent afterwards does not help.