Deuteronomy 21:12

then thou shalt take her into thy house, and let her cut off the hair of her head, pare her nails,

Some say the reason why you will bring her into your house, where she will shave is that perhaps you desire her on account of her hair — accordingly, you must shave it.

do her nails i.e., grow her nails, so that she may be repulsive in his eyes.

V’ASETHAH’ HER NAILS. “She shall ‘let them grow,’ [the reason being] that she should become repulsive.” This is Rashi’s language which accords with the words of Rabbi Akiba, 212. and so did Onkelos explain it [“and she shall let her nails grow”]. Now, according to their opinion the word v’asethah will be like ‘v’asath’ (and it shall bring forth) the produce, for “growth” is termed asiyah (doing). But in the Sifre 212. there is stated a proof to the words of Rabbi Eliezer [who explains ‘v’asethah’ her nails — and “she shall cut” her nails] from the following verse, and he [Mephibosheth] had neither ‘asah’ (dressed) his feet [i.e., cut the nails] nor ‘asah’ (trimmed) his beard. And this is indeed a great proof!
Therefore I say that these are all regulations of mourning, all connected with the expression, and she shall bewail her father and mother. Thus he commanded that she shall shave her head, similar to what is written of Job [when he heard of the death of his children], and he shaved his head, and so also, cut off thy hair, [and cast it away, and take up a lamentation]. So, too, the cutting of nails is a form of mourning like the shaving of the head. He states, and she shall put the raiment of her captivity from off her, that is to say, she shall don the garments of mourning, and she shall remain in thy house like a widow and not go outside at all, and she shall bewail her father and her mother, doing all this a full month, for such is the custom of mourners.
And in the opinion of our Rabbis 213. who say that all [these regulations] were intended to mar her beauty [the sense of the verses is as follows]: He commanded that she remove her beautiful garments, for [among] the heathens — accursed ones — their daughters adorned themselves in wartime in order to entice [the enemy] after them. She is to shave her head, which is considered a great disgrace, and pare her nails, for the custom of women is to let them grow and paint them with forms of stibium or other tints. And Scripture denotes the paring of a thing with the term asiah [“making” — ‘v’asethah’ her nails] because people cut the hair of the legs and the upper lip, as well as the nails when they grow [thus “making” and putting them in order].
It appears to me that [the term asiah in this connection] is an …

והבאת אל תוך ביתך, ”you will bring her inside your house.” According to the Talmud, tractate Kidushin folio 22, this means that after you had been intimate with her once, you must not do so again until after the procedures described in the verses that follow. Thus far the text in the Talmud as understood by Rashi. According to the version in the Jerusalem Talmud, however, even the first act of intimacy had been forbidden. The soldier cannot legally cohabit with her until all the details described in the Torah have been carried out. There are commentators who understand the words of Rashi, to not treat her harshly, to mean: “do not deprive her of the garments that she wore at the time of her capture.” [It is assumed that she had worn her best clothes so as to find favour in the eyes of any potential captor so that he would not kill her. Ed.] This is hinted at by the sequence of the verses here where she has been described as being brought into her captor’s house before undergoing a change of clothing in verse 13.