Answer
f her menses commenced while fasting, she can eat (not in public). If her menses stopped while fasting, she should abstain from eating, drinking, etc. but (in both instances) make up for the day by keeping a Qadhaa fast after Ramadaan. (Aalamgiri vol.1 pg.214; Rashidiyya)
And Allah Ta’ala Knows Best.
Mufti Ebrahim Desai
(Al-Mahmood 12)