PARIS: [Rory’s] never had sex. She’ll probably go to Harvard. She’s a shoo-in.
Shoo-in, North American informal English, meaning “a certainty, an easy winner”. The phrase dates to the 1930s, and originally referred to horse-racing When there was a predetermined winner in a horse race, jockeys would hold their horses and shoo the winner in – drive them in. Although the expression comes from corrupt horse races, today it doesn’t carry any stigma of cheating.
The Annotated Gilmore Girls 