Is this jostling of an employee’s schedule in violation of the FMLA?

Q: “Can a supervisor change an employee’s work schedule when they are on approved intermittent FMLA leave? The employee’s FMLA paperwork states that she must be on a particular shift because of a medical condition. The shift is 6:30 a.m. to 6:30 p.m. The employee arrives at work at 8 a.m. at least 2-3 days a week and states it is FMLA-related. The supervisor would like to change the shift from 6:30 a.m.-6:30 p.m. to 8 a.m.-8 p.m. The night shift employee has to remain, resulting in overtime for that employee. In addition, the same employee on FMLA will pick up an open shift when she has exhausted PTO to ensure 40 hours a week. Is she violating her own FMLA when she picks up an open shift?” – Anonymous, Virginia