Concurrently running FMLA leave, vacation time and short-Term disability

Q. Our policy requires an employee out on FMLA leave to run any accrued vacation or sick time concurrently with FMLA leave until that time is used up. (At that point, the FMLA leave becomes unpaid.) We also have a short-term disability (STD) policy that kicks in after seven consecutive days and lasts up to eight weeks. A pregnant employee recently requested 10 weeks of FMLA leave, starting upon the birth of her child. She currently has 3½ weeks of accrued vacation time. Can we require her to use up all of her vacation time once she goes out on maternity leave, even though she is also receiving STD payments? ...