Historically, there was no real law that prohibited widows from remarrying. There has never been a dynasty that forbade widows to remarry, because it's a very practical issue. It can't be done. If the law prohibits her from remarrying, how will she survive? The main economic labor force for ancient women came from men, so how would she live without them? The first principle is that she must finish the mourning period for her deceased husband. The second principle is that remarriage must be decided by her parents or parental figures. The third principle is that she is not allowed to take away her husband family's property, but can only take her own dowry.