Matthew Poole and continuators on Deuteronomy 22:21

21 Then they shall bring out the damsel to the door of her fathers house, and the men of her city shall stone her with stones, that she die , because she hath wrought folly in Israel, to play the whore in her fathers house: so shalt thou put evil away from among you.

Qu. Why should she die when her crime was onely Fornication, which was not punished in a woman with death, Exod. 22. 16, 17? Answ. Because there was not onely Fornication in this case, as Exod. 22▪ but this was accompanyed with deep dissimulation and injury to her Husband in the false profession of Virginity, and it might be presumed that she committed this folly after she was betrothed to him, and therefore so obstinately denyed it, as knowing the danger of it in that case; Or God ordered it thus for the honour and custody of the matrimonial bed from all defilement, that she, who being defiled before she was married or betrothed, and therefore not punishable by death, yet if she should presume to carry her defilement into the married estate with a pretence of Virginity, she should then be put to death.

Marginal references: Chap. 13. 5.