When a girl reaches the age of twelve or thirteen, the onset of menstruation signifies her capability for childbearing, marking her as a young lady, and her parents can start arranging a marriage, in preparation for her coming of age ceremony, followed by her wedding, and her roles as both wife and mother.
There are also those who start menstruating later at fourteen or even fifteen years old. Zhou Ning, at her age, should have had her menstruation long ago, but she is almost sixteen and it has not come. This is a big problem. Other girls have it, but she does not; no wonder she shrinks into herself, looking pale, dry-faced, utterly lacking the confidence that one her age should be brimming with.
Without menstruation, a marriage proposal cannot be entertained. If the groom's family realizes the underlying issue, they will certainly call off the wedding, or even accuse the bride's family of deception. This would lead to a loss of face and a ruined reputation.