Ignore her. She is not a client. A call to the client that got the friends and family deal might be notified that I'd the SIL does not stop harassing the store, the actual client will be banned from working with the store again. A restraining order for harassment might also be in order. Better yet, offer the SIL your Money-Back Guarantee, and refund her every dollar she spent after returning the offending pictures. When she returns the pictures give her the $0 back that she spent.