Is entering the Grand Mosque (Haram Makkah) while menstruating – due to ignorance and shyness – considered a grave sin, and what is its expiation?

Blood connected to yellowness or brownish discharge is considered menses as long as it does not exceed 15 days. A menstruating woman entering the mosque is a mistake, and the preponderant opinion is that it is not permissible for her to do so, and she must repent and seek forgiveness. If she performs 'Umrah while menstruating, her circumambulation (tawaf) is invalid because it was performed during menstruation, and the ritual running (sa'y) is invalid due to not being preceded by a valid circumambulation.