Does a woman have to go to the Mikva after consummating her remarriage? I know a woman needs to go after consummating her marriage the first time, but if she is no longer a virgin is it necessary to go after consummating her second marriage?
After the first time a woman experiences a biyah, it is common for her to bleed somewhat. In reality, this hymenal bleeding is dam makah (blood from a wound) and not uterine bleeding. In normal circumstances, dam makah does not render a woman a niddah; however, there is a rabbinic stringency that we treat hymenal bleeding (called dam betulim in Hebrew) similarly to dam niddah with just a couple of minor leniencies. We apply this stringency even when no hymenal bleeding was noticed because we assume that there was some amount of blood that we simply did not notice. Therefore, the first time a woman has relations, she goes to the mikvah.
However, a woman who was previously married and experienced biyah will not generally have further hymenal bleeding, so the stringency of dam betulim would not apply to her. Therefore, there is no need for her to separate from her husband after the first biyah, unless there actually is further hymenal bleeding.