I would like to know when a woman does not have a normal period and it comes for months, what does she have to do because she cannot pray?
In this case she will count ten days as menses, starting from the day which she thinks might be the habitual day.
In other words, if the woman sees that in the beginning, her menses used to start from the first week or second week, then when she experiences continuous menses she will look at that day or time it used to happen. From that day/time, she will now check ten days which she will consider to be her menses. After the ten days, she will take a compulsory bath (to come out of her menses) and will perform Salaah. She will continue to wash the blood off herself and make wuzu at the time of every Salaah, and thereafter perform Salaah until the days of her menses return in the next month. She would look at the time the menses came in the past to determine which day/date she can count from. Although she may be experiencing blood flow during these days, it would not be considered as her menses. This blood flow is known as Istihadha or abnormal bleeding. Upon the arrival of the date of her menses in the next month, (if the blood flow continues), then she will stop the performance of Salaah and count ten days as her menses. During this time, no salaah will be performed. If the blood flow still continues, then at the end of ten days she will take a compulsory bath again and begin to perform Salaah until the date of her menses comes in the next moth. She will continue in this manner as long as her problem exists.
And Allah knows best.
Mufti Waseem Khan
This answer was collected from DarulUloomTT.net, which is operated under the supervision of Mufti Waseem Khan from Darul Uloom Trinidad and Tobago.