It's literally what happened, though. Minus the pregnant part -- she got pregnant later, and the stuff about Rosa being agitating.
Claudette Colvin was the 17yo. Rosa Parks, who worked for the NAACP at the time, was selected as a more palatable figurehead.
For many years, Montgomery's black leaders did not publicize Colvin's pioneering effort because she was a teenager who was pregnant by a married man. While, the conventional story is that she was pregnant at the time of the incident, she actually did not become pregnant until later.[1] Words like "feisty", "mouthy", and "emotional" were used to describe her, while her older counterpart Rosa Parks was viewed as being calm, well-mannered, and studious. Because of the social norms of the time and her youth, the NAACP leaders worried about using her to symbolize their boycott.[2][3]
Claudette Colvin: "My mother told me to be quiet about what I did. She told me to let Rosa be the one: white people aren't going to bother Rosa, they like her".[4]