Can we switch a salaried employee to hourly to deal with pregnancy-related absences?

Q. Our office manager, who is pregnant, has begun coming in late two or three times a week due to morning sickness. Because she is a salaried employee, we know that we cannot deduct from her wages for partial-day absences. Can we change her position to one that is paid on an hourly basis until she returns from her maternity leave? ...