If it doesn’t exceed 15 days per month, this is her period and she must not pray when the blood is there until she sees her purity.
If it exceeds that, if her period was regular every month, she must consider the timing and stop praying  when the time of her menses is due.
If she didn’t have a fixed time every month, then she may act upon recognition of the characteristics of menses.

What should a woman do who has PCOS and is able to distinguish b/w menses and istihaza but has irregular periods so her cycle is not set sometimes it comes earlier than 15 days or takes upto 2 months however she is able to distinguish if it is menses. Can she follow her instincts?

Menstruation and post-natal bleeding | September 2, 2017 5:33 pm
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What is the status of a woman who frequently has prolonged brownish spots as discharge. Can she pray? Does she have to perform her ritual bath every time the discharge stops and reappears after a day or two?
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Please can you advise if a sister is teaching children in a room and the room is used for prayer as it is an old prayer building having carpets with musallah..cam she teach there on that floor when she is menstruating?