There were not so many women in my group, but there were 2 or 3 as I recall. Also, the bikes were all 125 ccs, so they were light enough and had low enough seat heights for even the most petite of women.
I have heard mixed reviews from women - some felt they were treated specially by the male instructors, others that they were treated too harshly. My g/f thought the instructors were fine, as did I. In fact, Dave (I don't know his last name) managed to impart the seriousness of the course and at the same time was hilariously funny (well, I appreciate dry wit).
Due to the serious nature of motorcycle instruction, instructors tend to be stern. Also, in order to be heard over the noise of the bikes and through helmets, instructors often seem to be yelling at students. Some folks take this personally, although they should not.
If you go in with the right attitude (i.e. Men - leave your ego at the door, and women - put on your "thick skin"), any MSF course is equally beneficial for both men and women. I would suggest that you take the course with her, even if you are an experienced rider. I did (took MSF with my g/f), and even after 5 years of riding, I found there was new stuff to learn.