What must a girl do who suspects that she did not fast some days of Ramadan in her childhood due to her ignorance of the obligation to fast, and she did not make up what she missed, knowing that she does not know the number of days she must make up?

If you doubt whether puberty has occurred, the default assumption is that it has not. If you are certain of puberty but doubt whether you fasted after it, there is a difference of opinion on this matter. The Hanafis hold that one's liability is clear and not burdened by such doubt. This opinion is suitable for those afflicted by obsessive doubts, to repel such whisperings. Therefore, no making up for missed fasts (qada') is required. According to the majority of scholars, you must make up for the days you doubted having fasted, but no expiation (kaffarah) is required because there was no breaking of the fast through intercourse.