Found this site that tells you about the Mikva. This is from it and may answer your question:
"Exactly a week from when the woman has established the cessation of her flow, she visits the mikvah. Immersion takes place after nightfall of the seventh day and is preceded by a requisite cleansing. The immersion is valid only when the waters of the mikvah envelop each and every part of the body and, indeed, each hair. To this end, the woman bathes, shampoos, combs her hair, and removes from her body anything that might impede her total immersion.
Immersion in the mikvah is the culmination of the Taharat Hamishpachah discipline. It is a special moment for the woman who has adhered to the many nuances of the mitzvah and has anticipated this night. Sometimes, however, the woman may be feeling rushed or anxious for reasons related or unrelated to this rite. At this point, she should relax, spend a few moments contemplating the importance of the immersion, and in an unhurried fashion, lower herself into the mikvah waters. After immersing once, while standing in the waters of the mikvah, the woman recites the blessing for ritual purification and then, in accordance with widespread custom, immerses twice more. Many women use this auspicious time for personal prayer and communication with G-d. After immersion, woman and husband may resume marital relations."