Heather Hills

Heather Hills is a teenager in Rodrick Heffley's grade. Greg Heffley has a big crush on her.

Rodrick Rules
In the second book she babysits Rowley while his parents were gone. She was later replaced by Leland.

Dog Days
In Dog Days, Greg always tries to impress her, but she barely pays any attention to him. She has a younger sister, Holly Hills, who Greg also has a crush on. She is a lifeguard at the public pool in Dog Days, and Greg attends to her every whim while there, but she pays him no mind, except when a kid vomits.

Trivia

 * In the online book, she is known as "Lori Matthews."
 * Why Leland was replaced as Rowley's babysitter is unknown, but uncharacteristically, in the online book, it states that she was fired for smoking outside Rowley's house after she had put him to bed.
 * Greg seems to have a thing for both Hills sisters.