Who is Lilly Fischman from Ham on Rye and what is their importance?

Lilly is a precocious teenager, who performs a sexual dance for the boys during biology. She later agrees to meet one of Henry's friends in an old car. Henry, the designated look-out, but all three are caught. Luckily, Henry dets off with a thousand demerits. Lilly and Pete are immediately removed from school.