Read this hardcover from the library in the late 70s. Teenage girl with dead mother, lives with her aunt or grandmother but spends summers with her dad. When girl is near the end of high school her dad announces he has a wonderful opportunity–he has to make a trip to Mars, and he can bring along one person, which will be her. She doesn’t want to go because she had her next few years all planned out and it will be a year or more before they get back. She sulks and yells, but is told she IS going. On board, her poor attitude does not win her any friends or allies among the people she meets. There is a small group of other children and young people on the ship, but she alienates them with her constant complaining and her attitude that people who live on Mars are backward and ignorant. One young man who is returning home to Mars takes on trying to improve her attitude as a personal challenge. When her father dies during the trip, leaving her with no return ticket, the young man’s family unofficially adopts her and helps her adapt to Mars. She enrolls in college there, and generally drops her snobbish, “Everything Earth is superior” viewpoint. I think at the end of the book she is faced with the one-time chance to return to Earth, or to stay with the people she has come to think of as her new family. There was probably a romance between the girl and the boy who “adopts” her.
I think it was shelved near the Beverly Cleary books, so author’s last name probably began with either C or a letter close to it.