I have told her a do not approve of any relationship beyond a friendship.
Right there you stated to her what is acceptable and what is unacceptable. SO the ball is in her court about this "friendship." How were you even made known that she had traveled with him? Or rather, how did the subject of him come up? And you're correct: it will be up to her to stop her A if she's having one. She will have to do that all on her own.
