When she got her period in Ramadan, she broke her fast and did not make up the missed fasts
Question

There is a woman who has reached the age of sixty. She was unaware of the rulings on menstruation for many years, during her childbearing years. She did not make up the fasts that she missed in Ramadaan, thinking that she did not have to do so according to what she heard from the common folk.
Praise be to Allah.She has to repent to Allaah from that, because she did not ask knowledgeable people. She also has to make up the fasts that she missed, fasting the number of days that she thinks she most likely missed. She also has to offer expiation for each day by feeding one poor person half a saa’ of wheat, dates, or rice etc., of the local staple food, if she is able to do so. If she is not able to feed the poor then she is not obliged to do so and it is sufficient for her to make up the missed fasts. 
And Allaah is the Source of strength. May Allaah send blessings and peace upon our Prophet Muhammad and upon his family and companions.