Was what the questioner did correct by performing ghusl and beginning to pray on the eighth day of her menstruation, which exceeded its usual duration, knowing that the blood is still flowing with the characteristics of menstrual blood? And is a full ghusl obligatory, or only wudu’ if it is istihadah and she has been cleansed of blood?

The maximum duration for menstruation is fifteen days. Therefore, any blood a woman sees during this period is considered menses. Accordingly, performing ghusl while blood is still flowing is incorrect. Rather, she must observe the period of menstruation until it completes fifteen days. If the blood flow exceeds this duration, then she is considered to be in a state of istihadah (post-menstrual bleeding).