Actually, the copy was found when our son was young, and I snatched it up because I had loved the book so much as a girl. Turns out a lot of people in my generation grew up loving this book and the high list prices found on used book sites attest to the high demand for a rare book.
Before Encounters With a Third Kind, before E.T., Star Girl is about an alien from outer space who is stranded on the Earth, and is found and befriended by children. The kids have a lot of adventures, partly because the girl, Mo, may speak the language but she does not understand the culture. And partly because the naive kids proudly announce they have found a girl who had fallen from a space ship, which of course gets the adults pretty worked up.
Mo is a beautiful girl with huge violet eyes and fine blond hair. At 87 years old, she appears to be 7 or 8 in human years. Her world is one of peace and plenty. The dissension among the children upsets her. She does not understand the concept that food must be purchased, or that bad behavior is punished. In Mo's world the children learn from glowing screens, and they love education! The only adult who treats them kindly is the librarian, a white-haired lady who truly loves children.
The kids need to get Mo to an open field where her father is expected to pick her up that night. They travel through woods and swamp, and just make it. Mo's planet turns out to be Venus. The round spaceships gather over the open field, where the adults, searching for this missing children, also gather. Mo's father, a tall man dressed in a human suit, thanks the children for their assistance to his daughter. He offers Mo's diamond necklace to the boy who led the group and cared for Mo. It will raise his parents from their poverty.
The author was a Jew who left Nazi Germany for America. He wrote books for adults, and several for children. The illustrator was Fritz Wegner and the translator was Kyrill Schabert.