What is the law if we have an ex-employee who will not hand over the business facebook page and has

put a post on there about her new place of business to get clients to go there instead?

The business facebook page is business property: if she will not hand it over and in fact has misappropriated it for her own use, she has stolen business property. You should file a lawsuit seeking declaratory judgment (a court determination) that it's your page and must be return to you; a court order requiring her to turn it over; and also seeking monetary compensation for the diversion of business (i.e. for lost clients or business). In the suit, which you will file on an "emergent" (think: urgent or emergency) basis to get into court faster, you will also seek injunctive relief with temporary restraints (e.g. a temporary restraining order) that she stop using the page (take it down) pending final resolution of the matter. Your lawsuit will be based on theft--which is something you can sue over as well as a crime--and "tortious interference with economic advantage"--interfering with your business through a wrongful or itself illegal means. Since filing matters on an emergent basis is more procedurally complicated than filing on a regular basis, and seeking declaratory relief and court orders is more complicated than seeking only monetary compensation, you are strongly advised to retain an attorney to help you. (Actually, if your business is an LLC or corporation, you *must* have a lawyer--only attorneys can represent LLCs and corporations in court.)