Her gender has nothing to do with what flex shaft she needs. Find a good fitter in your area, and have her fit. The whole works, too. Women's drivers usually have a lot more loft than men's, so the standard loft on the club probably isn't the best, either. A lot will depend on he angle of attack. With a swing speed of 90-92 mph, depending on the model, it is probably a men's regular or maybe even a stiff. It very, very much depends on manufacturer and model, however, so don't just go by the word, go by the manufacturer's recommendations. Her feel will enter into it too, and if she it used to an L flex shaft, she may not want to change too mcuh. Make sure she tries a senior (A) flex shaft or two, also. On the one hand, you want a shaft built to be most efficient for a certain swing speed and type (aggressive vs. smooth, etc.) but on the other if the feel is off, the confidence in the club will be very low, so you cannot discount the feel factor as well.
While your wife is getting a good fitting, you can too. Again, the loft and shaft will be fitted for you based on your particular swing.
If you can't find a good fitter in your area, there are some good people on this forum. Indacup is a sponsor of this forum and I am sure he will do his best to fit you as well as he can.