You should have access - either by mail or online - to an EOB from the insurance company that will outline the date of service, what service was provided, and how much they paid for it.

If the insurance company shows that they paid for a date that you did not see your therapist, then it is fraudulent billing. If she has had a third-party outfit that handles her billing, then she should follow up with the insurance company to make sure they are reimbursed for the claim submitted in error. If she actually submitted that billing, then I'd keep an eye on her.