What is the ruling regarding a girl whose menstrual cycle has become irregular, ranging from six to eleven days due to a hormonal imbalance? And should she wait three days beyond her usual cycle before performing prayer and considering herself to be in a state of istihadah (post-menstrual bleeding)?

The blood a woman sees during the period of possibility is considered menstruation. Her regular cycle may come earlier or later, or increase or decrease in duration. So, any blood a girl sees after the end of her customary period is considered menstruation, as long as it does not exceed fifteen days. If she sees menstrual blood for eleven days, it is menstruation. Similarly, any days of bleeding she sees in the following month are considered menstruation, as long as they are within the period of possibility and do not exceed fifteen days.