Katie O'Shea was a member of The Ultras
When Carrie is having her period she starts laughing. She is later seen in detention chewing her hair and looking bored. She was present in the calisthenic.
During the prom blood bath she is sprayed by the hose and later burned to death
According to IMDb, She is portrayed by Katie Irving. Who also wrote and singing two songs to the film ("Born to Have It All" and "I Never Dreamed Someone Like You Could Love Someone Like Me")