What should we do? It looks like employee used FMLA leave for elective surgery

Q. An employee told her supervisor that she needed surgery. We approved time off under the FMLA with the understanding that she would provide certification after the leave began. We later discovered that this “necessary” procedure was liposuction. Can we revoke approval of medical leave under the FMLA and convert sick hours she used to vacation hours instead? Can we fire her based on inappropriate use of the FMLA?