I also teach NRA Basic Pistol and I can say that there are many reasons to offer women-only classes. My wife took one, also taught by a female instructor, and had a great time, learned a lot and qualified for her CC application.
Women-only classes eliminate the husband/boyfriend factor which is not always positive.
Some women (note I said "some") are going to be really nervous. Being with other ladies will mitigate that.
Women will tend to ask important questions that they may not necessarily ask if they are in the minority.