Is the blood that came down on the woman five days after a Cesarean section, then stopped, and she resumed praying, then other blood came down on her two days later and continued for more than 12 days, postpartum bleeding (nifas), menstruation (hayd), or irregular bleeding (istihadah)?

The blood mentioned is postpartum bleeding (nifas (definition)), because the maximum duration of nifas is forty days, and any blood that returns during this period is considered nifas. The woman must stop praying, fasting, and everything else that a woman in nifas abstains from, until she sees purity or completes forty days. Her previous state of purity was valid.