You will have to file a legal action (lawsuit) against her, seeking a court declaratory judgment (determination) that the camper is yours as well as an injunction (court order) requiring her to turn it over to you. Once you have that, if she still refuses to do so, at that time you can get law enforcement (e.g. the sheriff) to help you. A lawyer can help you do this; if you want to do it yourself (pro se), contact the clerk of your court and ask for instructions and forms.