What must a girl do who completed the Ramadan fast at thirteen years of age, then broke her fast for four days due to menstruation out of shyness and told no one, and now eight years have passed since then; what should she do?

You erred by delaying the making up of the fast for the entire period. You must make up the four days you missed fasting, in addition to an expiation of feeding one poor person for each day. This is approximately two sa's of the staple food of the country for one or more poor persons.