Hadith.1992 - It was narrated from Al-Ays bin Al-Qasim:
"
I asked Abu Abdullah (as) about a woman who begins menstruating during Month of Ramadan before sunset.
Imam (as) said: 'She should break her fast as soon as she begins menstruating.'"
Man Lā Yaḥḍuruh al-Faqīh #418"Yes, she must break her fast, and if it is before sunset, she should break her fast."
As for a woman who becomes pure from menstruation...
Al-Kāfi #537“I once asked abu ‘Abd Allah (a.s.), about the case of a woman who experiences Hayd (menses) in the month of Ramadan before sunset. He (the...