ANSWER:

There is no expiation for this except to repent to Allah while showing deep remorse and to keep all those missed fasts of the past.

QUESTION: What should a woman do if she has not kept her skipped fasts(due to menstruation) after Ramadan, eversince her puberty? Does she have to keep all the skipped fasts of past 18 years? Or feed the poors? If to feed, then how many?