Answered by Ustadha Shazia Ahmad
Does a woman have to repeat those prayers that she prayed during her menstruation due to the fact that she assumed she was tahir (pure)?
Answer:
If one thought that she was pure, but was really menstruating, she does not have to make up those prayers. However, it is haram for her to be praying when she is not supposed to, and likewise, haram for her not to pray when she is supposed to. Ignorance of the rulings does not excuse her from her obligations and she should repent to Allah and take measures to learn the rules of menstruation.
And Allah knows best.
Shazia Ahmad