What is the ruling on repeating Sayyid al-Istighfar (the master of seeking forgiveness) 100 times as part of a collective dhikr for girls?

Sayyid al-Istighfar (the Master of Seeking Forgiveness) is a supplication of immense reward, mentioned morning and evening, and whoever recites it and then dies will enter Paradise. The general principle for unrestricted adhkar (remembrances) is not to restrict them to a specific number. However, there is no harm in designating a specific number for seeking forgiveness as a regular litany (wird), provided that one does not believe there is any special virtue in that specific number or that it is a regular Sunnah from the Prophet (peace be upon him). Rather, this should be done for the purpose of managing time, habituating the self, and consistently performing good deeds.