What will happen for a 15 year old living in PA who doesn't want to visit her father in another state and the custody order is in a 3rd state. Can the father have the order registered in his state unilaterally in order to enforce custody? Will PA or the originating state of jurisdiction be able to enforce it? How likely is this since she is already 15 and her father was abusive and threatened her the last time she had contact? She is very afraid of him.

What will happen for a 15 year old living in PA who doesn't want to visit her father in another state and the custody order is in a 3rd state. Can the father have the order registered in his state unilaterally in order to enforce custody? Will PA or the originating state of jurisdiction be able to enforce it? How likely is this since she is already 15 and her father was abusive and threatened her the last time she had contact? She is very afraid of him.
Is there a court order for visitation, or is it just for custody?

All court orders stay in the originating state until a change of venue is done through the court to change jurisdiction to another state. So yes, the originating state will be able to enforce visitation.

You need to file for a change of venue to your state then file to modify the visitation in your state. You'll need to provide the court with documented evidence of any past abuse etc. before a court will deny visitation rights to him. Sorry, but your daughter being afraid of him and not wanting to go most likely will not be enough to deny visition, so make sure to get all the documents you can before going to court.