"Is it permissible for a woman to pray Isha with the congregation in the mosque as a combined prayer if she attended for Maghrib prayer? "

"Praise be to Allah.

If a woman attends the congregation in the mosque and her family gathers due to rain, she is allowed to join the congregation, even though she is not originally obligated to join the congregation. Scholars have differed on this issue: some have said she should not join because she has no excuse to leave for the mosque, and some have allowed her to join as if she were in seclusion, to gain the virtue of the congregation. The favored opinion is that if a woman attends the congregational prayer in the mosque and they gather because of rain, then she may join them; however, in homes, women do not join the congregation.

And Allah knows best."