It's a lovely romantic youth novel that I read many years ago in German. It's about a girl who is part of a crew that is observing the development of other planets. They are from a very well-evolved planet and developed psychic powers already.
The idea is that all planets go through similar points of development. They observe a planet that is in the Middle Ages, but at the same time being colonised by another planet that is in a planetary colonialisation phase. So against her agenda, the protagonist is starting to help the planet defend itself against the industrial civilisation that is trying to conquer it.
She disguises her telekinetic powers as magic, meets a guy who she falls in love with, and together they try to stop the colonisation.