What makes Stargirl so interesting?

is actually a
girl named Susan, but she prefers to go by "Stargirl."  At her school, the other
students just want to fit in and be popular, but it becomes clear that Stargirl has no interest
in fitting in.  This sets her apart from the other students almost immediately.  She doesn't
wear makeup, and wears weird outfits every day. She decorates her desk at school and sings Happy
Birthday to kids she doesn't know.  At sports games, she cheers for the other team.  She doesn't
seemed concerned with being popular-she just wants to make everyone else around her happy.  Some
of the other students accept her, while others are wary of her and think that she's just doing
all of this for attention.