Laws vary state by state, but I know for sure that my state requires a minimum of 2 nights' stay after delivery. That is, barring any complications. If there were any problems, it is up to her doctor as to how long she should stay. If she is to have a c-section, it will automatically be a longer stay (again, in my state 5 days) because of the surgery. Best of luck to you both during this happy time!
