Deuteronomy 22:21

Quest. Why should she die when her crime was only fornication, which was not punished in a woman with death, Exodus 22:16,17 ? Answ. Because there was not only fornication in this case, as Exo 22, but this was accompanied 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 denied 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.