How can a woman know if she is still a virgin or has become a non-virgin after the first marital intimacy during her menstrual period?

It is not permissible for a Muslim man to have intercourse with his wife in her vagina while she is menstruating, and he must abstain from that until she becomes pure. It is permissible for him to enjoy the rest of her body, except for the vagina, during menstruation. If the husband fears he will not be able to control his desire, he should delay intercourse with her until she becomes pure.