Shepard will appear in the seventh episode of Season 1-- and ABC Family tells us she'll be having a friendly encounter with one of the girls ... but which one? You'll have to tune in.
Regardless of which girl it is, we bet the girls are psyched to have Sara on set. Star Lucy Hale tells us, "When I got involved in the show, I went and bought all of [the books]. I'm now on the seventh one ... I can't stop reading them. They're addictive."
Shepard is best known for her "Pretty Little Liars" Ya series books, but she also published an adult novel, "The Visibles," in 2009, which got positive reviews from Publisher's Weekly. We can't wait to see her foray into the world of her books at Rosewood High School.