Gemara

(Beraisa - R. Dosa): A captured woman may eat Terumah. Just because the captor put his hands on her, should she be forbidden to Terumah?!

Kesuvos 11b (Mishnah): If a girl above three was redeemed from captivity, her Kesuvah is 100. There is no Ta'anas Besulim.

13b (Beraisa - R. Yehoshua (to Chachamim)): Don't you agree that if witnesses say that a woman was taken captive, she is not believed to say that she was not defiled? Talking (seclusion with) a man is like being taken captive!

Chachamim: A captive is different, since most Nochrim are immoral.

27b (Beraisa #1): We accept testimony that a captive is Tehorah from even a woman or (most) relatives, but not from her son, daughter, slave or Shifchah;

(Beraisa #2): All are believed to testify for her, except herself and her husband.

36b (Mishnah): A captive who was redeemed does not receive a fine (if later she was raped or enticed);

R. Yehudah says, she retains her Kedushah (she is assumed to be a virgin).

(R. Yochanan): R. Yehudah holds like R. Dosa, who permits her to eat Terumah.

Objection (Rabah): R. Yehudah said that she retains her Kedushah, lest a rapist profit, but he could hold like Chachamim, who disqualify her from Kehunah! R. Dosa permits her to eat Terumah mid'Rabanan, but he could agree that she does not collect the fine mid'Oraisa!

Question (Abaye - Beraisa - R. Yehudah): A captured girl retains her Kedushah. Even if she was 10 years old, her Kesuvah is 200.

We cannot say that the reason is to prevent a sinner from profiting!

Answer: There, we are concerned lest men refrain from marrying her.

Question (Rav Papa bar Shmuel - Beraisa - R. Yehudah): A female convert must wait three months before marrying (to avoid doubts about fatherhood).

Answer (Rav Yosef): You cannot ask a question from a convert to a captive. A convert is not careful to avoid Bi'ah (before conversion), but a captive is.

Kidushin 64a (Mishnah): If a man said 'my daughter was captured and I redeemed her (she is forbidden to Kohanim)', he is never believed.

This is because he may not hand her over to captors.

Question: He can forbid her to Kohanim by marrying her to a Chalal!

Rishonim

Rif and Rosh (Kesuvos 13b and 3:4): The Halachah does not follow R. Yehudah.

Rambam (Hilchos Isurei Bi'ah 18:17): The Isur of every Safek is mid'Rabanan. Therefore, Chachamim were lenient about a woman taken captive.

Mishneh l'Melech (1): The Gemara asked that one should be believed to say that his daughter was captured, for he could marry her to a Mamzer and disqualify her from Terumah! If a Shevuyah is forbidden only mid'Rabanan, perhaps the father wanted to forbid her only mid'Rabanan, but not that she would be lashed for eating Terumah! It seems that all agree that the Isur Shevuyah is mid'Rabanan. Chachamim were lenient about it, for captors do not disgrace captives so much. Even those who forbid a Safek mid'Oraisa only mid'Rabanan, it is more stringent than a Stam mid'Rabanan.

Avnei Milu'im (7:3): The father may not give her over to a Mamzer for Bi'as Isur. He may only be Mekadesh her and send her to Chupah. Chupah with a Pasul disqualifies only mid'Rabanan!

Question (Sha'ar ha'Melech 24): According to the Rambam, he can marry her to a Mamzer mid'Rabanan, even according to R. Akiva! This is not difficult for Rashi, for perhaps the father wants to disqualify her mid'Oraisa. The Rambam cannot say so, for he forbids Shevuyah only mid'Rabanan!

Answer #1 (Sha'ar ha'Melech): Isurim mid'Rabanan do not disqualify her.

Answer #2 (Avnei Milu'im 7:3): The father may only be Mekadesh her and send her to Chupah. Chupah with a Mamzer mid'Oraisa disqualifies only mid'Rabanan. Chupah with a Mamzer mid'Rabanan does not disqualify at all!

Pri Chodosh (YD 110 Beis ha'Safek DH v'Im Tomar v'Ha): The Rashba can say that we are lenient about a Shevuyah because she disgraces herself to the captors. Alternatively, the Chazakah is that she was not defiled.

Kovetz Shi'urim (Kesuvos 26(73)): Why does the Rambam say that Chachamim were lenient about Shevuyah because Sefekos are only mid'Rabanan? Even if they were mid'Oraisa, a Shevuyah has Chezkas Heter! The Rambam holds that there is no Chezkas Heter, for most Nochrim are promiscuous. A Shevuyah's Kesuvah is only 100, and one who raped her does not pay a fine, for we assume that she was defiled. We cannot attribute monetary laws to stringencies mid'Rabanan. Rather, it is a Safek mid'Oraisa. Regarding money, ha'Motzi mi'Chavero Alav ha'Re'ayah. Tosfos holds that mid'Oraisa the Chazakah helps, even to make others pay money, for she makes herself repulsive to the captors. Tosfos ha'Rosh holds that the Chazakah does not force others to pay.

Tosfos (Kesuvos 36b DH v'Elu): Mid'Oraisa, a Shevuyah does not have Chezkas Be'ulah. Everywhere, Chachamim were lenient about a Shevuyah. Nevertheless, there is no fine for her. Chachamim made her like a Be'ulah in every way, lest she marry a Kohen.

Noda bi'Yehudah (EH 1:66): Tosfos in Kesuvos (26b DH Anan) and Kidushin (66a DH Mai) forbid Shevuyah to a Kohen mid'Oraisa. Tosfos Kidushin 12b (DH Im) connotes that it is only mid'Rabanan. Really, it is a Safek mid'Oraisa. The Rambam holds that all Sefekos are mid'Rabanan, but other Poskim forbid mid'Oraisa. A Shevuyah lost her Chazakah, for most Nochrim are promiscuous. Chachamim were lenient because she makes herself repulsive. Kesuvos 13b says that (it is as if) there are witnesses about a Shevuyah (that she was defiled). Without a decree, it is a Safek Isur Torah. Chachamim decreed to make it like Vadai, like the Shach (YD 110 Klalei Sefek-Sefeka 17,18) says about cheese of Nochrim. No Gemara explicitly says that Chachamim decreed. Perhaps mid'Oraisa we rely on Chazakah, and Chachamim decreed to make it a Safek. If so, they decreed only for lineage, about which we are stringent, but not for fines or Kesuvah. Tosfos says that we decreed about a fine, lest a Kohen marry her.

Suggestion: If mid'Oraisa it is a Safek, even without a decree she does not receive a fine!

Rejection (Noda bi'Yehudah): Due to the decree, if she seized the money she must return it. However, we can say that seizure of a fine never helps.

Poskim

Shulchan Aruch (EH 7:1): A Shevuyah is forbidden to a Kohen. She is a Safek Zonah, lest a Nochri had Bi'ah with her. If a witness says that she was not secluded with her captor, she is Kosher to Kehunah. Even a slave or relative is Kosher for this testimony.

Beis Shmuel (1): If she was married to a Kohen, she must leave. A single woman who was Mezanah is believed to say that the Bo'el was Kosher, and may marry a Kohen. She checks (the Bo'el) before having Zenus. Even though Shevuyah is only a Safek, and we forbid a woman to her husband only through Kinuy and seclusion, this is a stringency of lineage of Kehunah.

Rebuttal (Shevus Yakov 3:120): We concluded that a woman checks only for marriage! Perhaps compared to one who marries, one who is Mezanah does not check, but compared to a Shevuyah, she checks. We can distinguish Zenus from a Shevuyah without this. Most captors are Pasul, and Nochrim are promiscuous, so it is as if she Vadai had Bi'ah. Chachamim were lenient about testimony for her, but we cannot extrapolate. She must leave a Kohen. Maharashdam (EH 235) says that nowadays, a Kohen is Safek, for he cannot prove his lineage. He is permitted a Shevuyah mid'Rabanan. The Maharit (149) and Chut ha'Shani (17) disagreed. I (1:93) defended the Maharashdam, but I am unsure about Shevuyah. Chachamim were stringent about her regarding lineage, since Nochrim are promiscuous.