2,138. Immersing Before Marriage
Hilchos Issurei Biah 11:9
Continuing from the previous halacha, when a girl agrees to be married, she must count seven clean days after giving her consent. After that, she (must immerse in a mikvah and is then) permitted to her husband. This is because she might have had desire for a man and expelled a drop without her knowledge. She must wait these seven clean days after agreeing to marry whether she’s an adult or a minor. After these days, she immerses in a mikvah and may engage in marital intimacy.
Hilchos Issurei Biah 11:10
All of the aforementioned are stringencies that Jewish women accepted upon themselves since the Talmudic era and a person is not permitted to act counter to these practices. Therefore, any women who agrees to marry may not do so until she counts seven clean days and immerses in a mikvah. If the groom is a Torah scholar, then she may marry immediately and count the seven days and immerse after the wedding because a scholar will know that she’s prohibited and not approach her for intimacy until after she immerses.