If she moves out of the state without a court order, she could be found guilty of parental kidnapping.  Mexico is a party to the Hague Convention, an international treaty, that would make the West Virginia court custody order enforceable there, and once caught, she would be forced to return the child to the state.

There are two better alternatives.  One would be to move as far away as possible, but still inside West Virginia.  Most judges don't have a problem with that.  The other is to apply for permission to move, with the children, to another state, where she would have better employment opportunities or family support, or something along those lines.  Either way, making men like the one you describe drive for a couple hours either way, rather than just across town or so, often leads to their parenting urges fading, sooner or later.