Good Girl Bad Blood isn't based on a true story. It's a work of fiction that takes you on an imaginative journey without drawing from actual events or people.
In some ways, it could be considered true, but often in such stories, details are exaggerated or fictionalized to make it more engaging for the audience. So, it's a mix of truth and creativity.
One way is through her language. If she begins using vulgar or disrespectful words more often, it could be a sign of transformation. She may also become more secretive about her activities. For example, she doesn't tell her parents or old friends where she's going or what she's doing. Her grades might also start to drop significantly. This could be because she's more interested in other things like partying or getting involved in minor delinquencies rather than studying.
A sense of rebellion can also be a factor. Sometimes, a good girl might feel restricted by rules and expectations, and she rebels against them, turning into a bad girl. For example, if she has overly strict parents, she might go against all they stand for. Also, a major life change like moving to a new place or experiencing a trauma can make a good girl abandon her good - girl ways and become bad. She might lose her sense of self and purpose and start making bad choices.
Peer influence is a common factor. Just like in the story I mentioned before, a good girl can be easily influenced by the wrong crowd to become bad. Another factor could be family issues. If a girl doesn't get enough support or love from her family, she might turn to bad behavior as a form of rebellion.
There could also be a male character who is caught in the middle of the good girl and the bad girl. He might be attracted to both of them for different reasons. He could be a jock who is used to getting attention from girls, but the good girl and the bad girl present him with different challenges. He has to decide which one he really wants to be with, and this decision could be based on his own growth and values.
One main theme could be the contrast between good and bad. It might explore how different characters with good or bad traits interact and influence each other. For example, the 'good girl' might be influenced by the 'bad girl' to step out of her comfort zone in a positive or negative way.