Katie is a love interest to Will in The Inbetweeners 2.
Katie is a free-spirited English girl who backpacks across various countries in order to get more in touch with herself. In truth, she's just another spoiled rich girl playing hippy until she feels ready to grow up.
Will and Katie used to go to prep school together. When they meet up years later, Katie kisses Will on the mouth, which convinces Will to follow her on her cross-country tour of Australia. Katie tries to have sex with Will, who tries to decline as they're in a communal bedroom with Jay watching them. One of Katie's friends catches them together an immediately assumes that Will tried to rape her, which isn't helped by the fact that Katie was too drunk to remember anything.
After Will ditches his friends to spend more time with Katie and her hippy-clique, he begins to realise that Katie's not as deep as she claims to be. After she kisses Ben right in front of Will and tries to justify it as something deep and spiritual Will decides he's had enough and shames her for essentially letting her hormones think for her.
Ben is a pampered rich boy who believes he's a deep and spiritual person when he's actually quite smug and pretentious. Katie's aware of this but still likes him; not because of his personality, but because she can't control her lust. After Will tells them off for being so self-obsessed, Ben and Katie have sex in a bedroom that they share with Will, with Ben saying "I never lose!" over and over.