Need help finding another book please!!?

I also read this book around the same time, 1977 to 1980, the main character in the book was a girl nicknamed Rusty, I think her real name was Rosalind or something like that. Anyway, she had red hair and freckles that she hated so much, she was in high school. Her parents adopted her, someone left her on their doorstep. Her older brother nicknamed her "Door Step Dotie" when they were small. She was angry with him for quitting baseball, her father and her wanted him to go back, he didn't want to because he was getting tired of it. Of course there was a situation where she liked this boy. She also had a younger brother, making fun of her red hair and freckles. That is all I can remember right now. Can you help on this one?