Sherry Becker is a high school ex-girlfriend of Jerry Seinfeld. He reconnects with her in "The Library", since he remembers reading an overdue library book with her in 1971, which he still has yet to return in 1991. She clarifies to him that it was an entirely different book that they read together.
The young Sherry Becker (shown in a yearbook photo and a flashback) is played by Kathleen McClellan who returns 6 seasons later to play Melissa, Jerry's girlfriend who doesn't know the difference between "good naked" and "bad naked" in The Apology.