Admittedly, Carrie has a righteous cause -- to avoid war with the Middle East -- but to that end, she agrees to poison Saul in an effort to get the name of his Russian asset, to give to Yevgeny Gromov (Costa Ronin) in exchange for evidence that may prevent a nuclear war.
All the other girls were pretty, popular, happy; they basically were idealistic teenage girls. Carrie was the opposite: un-attractive, unpopular, unhappy. She was everything the other girls weren't, and she was also everything they feared, and everything they never wanted to be.