Your spouse does not have to be covered under your insurance policy, but will not be covered if she does drive the car, assuming he or she lives in your house.
If , for some reason, one spouse has a poor driving record and has no need to drive a particular car, you may be able to save some money by not listing that person on the car. It normally will not be too much extra to add another person on a car, but it is still a waste of money if that person never drives the car.