When exactly do women require Ghusl?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.

Women require Ghusl in the following two cases:

1-     After intercourse when the two private parts meet [when the top of the penis is inserted in the vagina] even if the man does not ejaculate, both of the man and woman are obliged to perform Ghusl.

2-     If a woman ejaculates either by having a wet dream or because of foreplay.

The evidence about the first case is the saying of the Prophet : "If a man sits between her legs and inserts his private parts in hers, then it is an obligation on them to perform Ghusl." [Al-Bukhari and Muslim] The narration reported by Muslim reads: "Even if he does not ejaculate." The Prophet further said: "If the two private parts meet and the male inserts his private parts in the woman’s, then they must perform Ghusl."

As regards the evidence on the second case: It is confirmed that Umm Salamah narrated that Umm Sulaym came to the Prophet and asked him: "O Prophet of Allaah, Allaah is not shy of the truth, is a woman obliged to perform Ghusl if she has a wet dream? The Prophet, sallallaahu alayhi wa sallam, replied: "Yes, if she sees the (white) discharges.” So Umm Salamah laughed and asked in amazement: “Does a woman have wet dreams?” He replied: “Yes, how is it then that her child resembles her?" [Al-Bukhari]

Furthermore, Anas narrated that the Prophet said: "If a woman finds in her dream what a man finds (wet dreams), then she has to perform Ghusl." [Abu Daawood] 

Allaah Knows best.