How can one distinguish between menstrual blood and abnormal bleeding (istihadah), especially when the bleeding continues for long periods and the woman is unable to discern the characteristics of menstruation? And is it permissible for a woman in this state to get married?

If you are a woman experiencing metrorrhagia (istihada) and you see menstrual blood for 9 days, then it stops, and you are not able to distinguish (between menstrual and non-menstrual blood):

1. First Opinion: You consider the 9 days as menstruation and then perform ghusl (ritual bath). Anything beyond that is considered istihada. 2. Second Opinion (Majority): You are considered "perplexed" (mutahayyirah). Therefore, you observe 6 or 7 days of menstruation each month by estimation (based on what you deem most resembling menstrual blood). 3. If the timing is the same for you and you cannot determine it: You observe these days from the beginning of the month. In summary: You abstain from prayer for 6 or 7 days, as is the usual habit for most women. Then you perform ghusl and make wudu (ablution) for each prayer, and you have the rulings of ritually pure women. You may get married, and your husband is permitted to have intercourse with you during the period of istihada.