Ruling 417:
If a fasting woman becomes mustaḥāḍah after ʿaṣr prayers and she does not perform ghusl until sunset (ghurūb), her fast is valid without any problem.
-Ayatullah Sistani, Practical Laws of Islam, Purification (Taharah)
Purity: Fasting and Istiḥāḍah After ʿAṣr Prayer
Practical Laws of Islam as per the teachings of Ayatullah Sistani
