What is the ruling on one who prayed with blood that she thought was the blood of fasad (post-childbirth bleeding), but it later became clear that it was menstrual blood, and is there anything upon her after she prayed for three days while menstruating?

The default rule is that any blood discharged by a woman is menstrual blood, unless it exceeds 15 days or she sees it before the minimum period of purity between two menstruations has passed (15 days according to the majority of scholars, and 13 according to the Hanbalis). The questioner erred in issuing a fatwa for herself, and she must repent for that. However, there is no sin upon her for the prayers she performed during the days she considered as menstruation, due to the lack of intentional transgression.