What should a woman do if she becomes dry from menstruation, then blood returns an hour later, knowing that she sometimes sees dryness and sometimes the white discharge?

If a woman sees purity by one of its two signs (dryness or the white discharge), she must perform ghusl (ritual bath). If bleeding resumes after that, within the menstruation period, it is considered menstruation, and she must perform ghusl after its cessation. Some scholars permit waiting half a day or a full day after seeing purity through dryness to ensure the cessation of blood. There is no harm in adopting this view as a facilitation, but the prevalent ruling is to perform ghusl promptly.