Must a Kallah wait five days after her period prior to beginning Shiva Nekiyim?
No. A Kallah upon having a period prior to her wedding is not required to wait five days prior to beginning her Hefsek Taharaha, and rather as soon as the bleeding ends she can perform the Hefsek Taharah and begin her Shiva Nekiyim. However some are accustomed for the Kallah to wait five days. Practically, one is not required to wait five days unless the community custom is to do so, although some suggest waiting five days as a matter of Chinuch. In all cases that waiting five days would cause the Kalla’s seventh day to fall on the day of her wedding and certainly if it would cause her Mikveh to be delayed until after the wedding, she is not to be stringent to count five days even if that is the community custom.
 Taz 196/7; Shach 196/20; Sidrei Taharah 196/23; Degul Merivava on Shach 196/20; Piskeiy Dinim 196/28; Taharah Kehalacha 9/4; Shiureiy Shevet Halevi 196 p. 298
 The reason: As she does not contain any Zera of her husband and hence the entire reason for waiting five days is irrelevant. [Poskim ibid] Furthermore, she was already a Niddah beforehand and is hence similar to a woman who saw a new period during her Shiva Nekiyimn in which case she is not required to wait five days. [Degul Merivava ibid]
 Custom brought in Shach ibid; however see Degul Merivava who establishes the custom only in a case of a woman who was Tahor beforehand, such as a young girl who now received her first period.
 See Shach ibid that although the custom has no source in any Posek, and in his opinion it is incorrect to be stringent, nevertheless one may not be lenient in front of a community that is stringent, unless it is a time of need.
 Shiureiy Shevet Halevi ibid
 Shach ibid; Shiureiy Shevet Halevi ibid