If a woman does not menstruate for a few months, she does not have any
vesatot since she does not have a new menstrual flow from which to calculate her new
veset days. The exception to this rule is a woman who had a
veset kavua for the Hebrew date, in which case the couple would continue to separate on that Hebrew date until it passes three times without incident.
If you are in this situation, it is advisable to check in with your health care provider to ascertain why menstruation has stopped.