Review past practices to judge FMLA leave request

Q. We're a 24/7 office. Some employees rotate shifts, but our night employees typically work the same shift. After one of our employees gave birth, she asked to be placed on the night shift. We granted her request, but now she says medical reasons require her to be off for five days in a row. We put her back into the regular shift rotation, but she claims her FMLA rights are being violated and wants all employees to rotate shifts, even the night employees. Do we have to do this? —M.L., Ohio