What is the ruling on the fast of a woman who performed ghusl and intended to fast while she was menstruating on the first days of Ramadan, due to her not knowing the signs of purity, then she became pure? And what is the ruling on the fast of a woman from whom menstrual blood was discharged before or after iftar on the last days of Ramadan?

Your fasting on both days is valid because you did not see any blood after performing ghusl (definition) on the first day. As for the last day, you saw blood after Maghrib, and you were not certain that it had appeared before Maghrib. When something is likely to have occurred in one of two time periods, it is attributed to the latter of them.