What does the Torah mean when it says "Im Ra'ah be'Einei Adonehah ... "?
Rashi (citing Kidushin, 19b): The Torah means to say that really he ought to betroth her, as the money he paid for her was meant to serve as Kidushin money. 1
Ramban: Once a master says that he will be marry her, her father should redeem her immediately, since the sole objective of selling one's daughter should for marriage.
What does "v'Hefdah" mean?
Rashi, Ramban and Rashbam: He helps her father to redeem her, by accepting from him the balance based on how much he paid for her and how many years remain of the six years that he purchased her for. 1
If for example, he purchased her for a Manah and two years have passed, the father pays him two thirds of a Manah, and she returns home (Rashi).
What does the Torah mean when it writes "l'Am Nochri Lo Yimshol ..."?
Rashi: It means that her master and her father may not subsequently sell her to anybody else.
Ramban #2, Seforno: It refers to her father, who is prohibited from subsequently selling her a second time.
Even though the Torah (in Vayikra 25:47) specifically permits an Ivri to sell himself to a Nochri.
Although Rashi's explanation conforms to the Gemara in Kidushin, 19a, the Ramban queries Rashi's translation of "Am Nochri". (See Ramban, who finally ascribes the Gemara's ruling to the words "be'Vigdo vah", as if it had written "Lo Yimshol" twice).
What does it mean "b'Vigdo Vah"?
Rashi: Her master betrayed her by not marrying her, and her father, by selling her 1 to this man [who will not marry her].
Rashbam: Her master betrayed her, for he should have married her. 4
Kidushin 18b: Once her master put his garment over (married) her, he may not sell her.
Rashi writes that he helps her father to redeem her, through accepting the balance based on how much he paid for each year. Why is this called helping? It is proper to pay the value of her remaining labor!
Moshav Zekenim: The master reduces from the balance based on the remaining years. He cannot pardon the redemption, i.e. totally, but he can pardon part.
Gur Aryeh: The master owns her Guf. Therefore, according to letter of the law, he should not deduct due to the labor she did. 3
Sefer ha'Chinuch, Mitzvah 44: The money paid for the remaining labor was with her [father, and he was able to profit from it]. The master may not take compensation for this.
For very young girls, their labor is worth less than the cost of feeding them! (PF)
Da'as Zekenim says that this is why Rashi calls this Gir'aon Kesef. I do not understand this. Gir'aon merely means reduced. We say that also Eved Ivri is redeemed through Gir'aon Kesef, even though often his first years are worth more than his latter years, e.g. if he is old! (PF) According to Rashi (Kidushin 20a), an Eved Ivri is redeemed based on the current value if the price of labor declined. An Amah is equated to an Ivri, but perhaps not for this, e.g. if in spite of the decline, her current value is now more because she is older.
Just like one who sells a house in a walled city, and redeems it, does not deduct the rental value that the buyer enjoyed, for it was a sale, and not a rental. (PF)