Rashi on Deuteronomy 21:13/רש"י על דברים כ״א:י״ג

1והסירה את שמלת שביה AND SHE SHALL REMOVE THE RAIMENT OF HER CAPTIVITY — the reason is because these are fine clothes, for the women of the heathen peoples adorned themselves in time of war in order to lure others (the enemy) to unchastity with them (Sifrei Devarim 213:1).

2וישבה בביתך AND SHE SHALL DWELL IN “THY” HOUSE — [not in the women’s apartments, but] in the house which he constantly uses: when he goes in he stumbles upon her, when he leaves he stumbles upon her (i.e. he cannot avoid meeting her constantly and the novelty of her beauty wears off); he sees her endless crying, sees her neglected appearance — and all this in order that she should become repulsive to him (Sifrei Devarim 213:2).

3ובכתה את אביה AND SHE SHALL WEEP FOR HER FATHER [AND HER MOTHER A FULL MONTH] — Why all this? In order to make a contrast — that while the Jewish woman (the captor’s Jewish wife) is gladsome, she should be downhearted, while the Jewish woman adorns herself, this one should bear a neglected appearance (Sifrei Devarim 213:5).