The obvious main character would be the girl who experiences the wedgie and loses her glasses. There could also be a bully who gives her the wedgie in the first place. Maybe this bully later has a change of heart and helps her look for her glasses.
Perhaps in the fanfiction, the girl is a bit of a clumsy character. She gets a wedgie, which causes her glasses to fall off and break. This then sets off a chain of events where she has to get new glasses. But she's worried about what people will think because of how she lost the old ones. She might have to save up money for new glasses and in the process, learn to be more careful.
The girl without glasses is the central figure. There may be an antagonist like a school bully who constantly teases her about her wedgies and her glasses - free look. Then there could be a wise old janitor who gives her advice on how to deal with the bullies and how to embrace her new self. There might also be a group of girls who initially exclude her but later come to accept her as she shows her true character despite the physical changes.
In a fanfiction setting, the girl who tripped and lost her glasses could be a magical being in disguise. When she tripped, it could be a sign that her powers were about to be revealed. For example, she might be a fairy whose glasses were enchanted to hide her true identity. Losing them could lead to a series of adventures as she tries to retrieve them before the wrong people find out who she really is.
The girl could be a young student who was abducted by bullies. The bullies tie her up, and during the process, her glasses are lost. A kind teacher or a fellow student who stands up to bullies could be the one to rescue her. They would then help her look for her glasses, which are important for her to see clearly in class.
Perhaps the plot revolves around how this 'wedgie girl' without glasses has her appearance change so much that it affects her relationships. Her old friends might not recognize her at first, and she has to re - establish those bonds. Also, it could be that she becomes the target of a bully who likes to pick on her new look, but she stands up for herself in ways she never did before because of this new - found sense of self without her glasses.
A kind - hearted fellow passenger could help her. Maybe someone who is uninjured and has a good sense of orientation in the chaotic post - crash scene.
In a detective - themed fanfiction, the girl is tied up by the criminal she was investigating. She loses her glasses during the scuffle. The detective protagonist has to piece together the clues she left before being tied up, while also looking for her glasses which might hold some vital evidence. As he searches for the glasses, he gets closer to finding the truth and rescuing the girl.
Maybe she would be in a state of panic and confusion after the crash. Without her glasses, she might have trouble seeing clearly which could add more danger to her situation. For example, she could misjudge distances while trying to find an exit or other survivors.
Maybe it's a group of thieves in a fantasy - like city. The girl witnesses them stealing from an old lady and decides to intervene. She takes them on and manages to beat them up, but her glasses are knocked off during the fight. The thieves could be part of a larger criminal organization that might come after her later for interfering.
The fanfiction could focus on how the girl copes with losing her glasses while being missing. She might use other senses more acutely. Like, she listens more carefully to the sounds of the forest to avoid danger. Also, the discovery of her lost glasses by someone else could be a turning point in the story, either leading to her rescue or more complications.