Rebecca
From The Big Bang Theory Wiki
Rebecca is a little girl who is reading Curious George books in the bookstore where Sheldon buys his copy of Stu the Cockatoo is New at the Zoo. Sheldon starts talking to her about their going to the zoo together, unaware that his friendliness would be misinterpreted. Leonard hustles him away from Rebecca and out of the store ("Don't look, there's cameras!").
Rebecca is played by Jade Zdanow.