What is the ruling on purity for a girl whose menstruation is irregular, and she asks about the duration of her period and the signs of purity, and how she can distinguish between discharge, yellowish discharge, and white discharge, and is turbid discharge after the cessation of blood considered part of menstruation?

The maximum period for menstruation is fifteen days. If the bleeding, along with any yellow or brownish discharge connected to it, exceeds this duration, then the woman is in a state of istihadah (non-menstrual bleeding). A woman recognizes her purity by one of two signs: complete dryness or the white discharge (al-qassah al-bayda'). Yellow or brownish discharge is considered menstrual blood only if it occurs during the usual period or is connected to the bleeding. If the bleeding stops with complete dryness, the woman is pure and must perform ghusl (ritual bath), and she should not pay attention to any yellow or brownish discharge she sees thereafter, as long as it is not connected to the blood.