How does one perform ghusl for menstruation and major ritual impurity (janabah) together, especially after having performed ghusl for menstruation and doubted its validity, then experiencing janabah and seeing what is believed to be menstrual blood again?

If a woman sees purity by one of its two signs: complete dryness or the emission of the white discharge, then ghusl becomes obligatory upon her. It is sufficient in ghusl to circulate water over the entire body with the intention of purification. A single ghusl is sufficient for both the impurity of menstruation and janabah if they occur together after purity from menstruation has been attained.