Is expiation (kaffarah) obligatory for one who broke her fast on the seventh day of her menstrual period, assuming she was still menstruating, and then realized on the same day that she had become pure, knowing that she did not intentionally break her fast?

If a menstruating woman experiences purity before Fajr, she is obligated to fast that day. If she was not aware of this, there is no sin upon her. If her purity becomes clear during the day, she must perform ghusl (definition), refrain from eating for the rest of the day, and make up that day. There is no kaffarah (definition) (expiation) upon her. Kaffarah is only required for breaking the fast through sexual intercourse according to the majority of scholars. Even those who mandate it for reasons other than sexual intercourse do not mandate it in this case, as there was no intentional violation of the sanctity of the month.