What if a sister didn’t know that when you are on your periods you can’t fast but once the Ramadhan is over you have to do it’s qaza, and didn’t perform any of her qaza?

Does she have to perform all the qaza now? And also does she have to give the kaffara for all the fast that she missed ?
How should she calculate all of this ?

She must do the qadhas and for those fasts missed previously, she should pay kaffara e takhir which is 750 grams of food to a poor person for every fast missed