I am looking for a Science Fiction novel, possibly for older children or young adults not certain of when it was published but possibly 70s-80s. I only remember vague bits of the plot so I hope I got it right.
A girl is on a spaceship with her scientist father observing an 'uncivilized' planet and its peoples. The father goes to the planet to get data and the girl also sneaks after him and accidentally reveals herself to a young man. Because she is dressed oddly and uses telekinesis he believes she is a witch or a goddess.
The father finds out and they decide to let the man believe she is a witch and she sets 'quests' for him such as learning to levitate a cup using telekinesis. They take the young man to their ship and try to teach him telekinesis using some sort of training program. Then other people arrive on the 'untouched' planet with polluting space ships and weapons and start to enslave the natives. The father and daughter help the young man to use his new telekinesis to get rid of the bad people.
It is implied that all three races are humans-the 'uncivilized natives' are ancient humans, the war-like humans have just left Earth and started claiming other planets, the and father and daughter are part of the far future enlightened and peaceful humans.