If she is at the end of the time of her usual period, once she sees dryness, she should make ghusul. But if she saw dryness two or three days earlier, she should wait at least for 12 hours to be sure.

Period ends either by complete dryness or white discharge. When white discharge comes it is obvious period has ended. But if there is dryness when she inserts cotton for first time has period ended? How long does she has to rely on dryness doesn’t blood comes and stops? If she sees dryness first time and does ghusl then she sees blood or yellow or brown discharge did that dryness end period