How are the days that my mother did not fast due to menstruation to be compensated for, considering she was unaware of the obligation to make them up, and do I owe expiation for the days I did not fast for the same reason?

One who omits an obligatory act out of ignorance incurs no sin in the afterlife. However, in this life, your mother is required to make up for what she missed. To excuse this, it is more appropriate for you to fast on her behalf for the days she missed, based on the Prophet’s (peace be upon him) saying: "Whoever dies owing fasts, his guardian should fast on his behalf." If you do not fast on her behalf, then feed a poor person for each day (approximately 750 grams). This fasting by the guardian is considered a recommended act. As for you, you must make up for the fasts you missed due to menstruation, along with an expiation for delaying (feeding a poor person for each day).