What is the duration to be considered for the menstrual cycle, and is the brown discharge counted as part of menstruation after the bleeding stops, given that the cycle was 8 days in adolescence and is now 12 days?

The maximum duration of menstruation is fifteen days, and anything beyond that is considered irregular bleeding (istihada). If a woman sees blood for eleven or twelve days, she is considered menstruating for the entire duration. As for the days interspersed within this period when the bleeding stops, the fatwa adopted by us is that these are days of purity (tuhr), so she should perform ghusl (ritual bath) and pray. Then, she stops praying if the blood returns. The brownish discharge during the days of menstruation is considered menstruation, as it is a turbid discharge during the menstrual period. However, after purity, turbid and yellowish discharges are not considered anything (i.e., they do not invalidate prayer or require ghusl).