Holly Hills

Holly Hills is Heather Hills's little sister, and according to Greg, one of the most popular girls in his year.

The Last Straw
She has made an appearance in the original and The Last Straw, and is briefly mentioned in the credits to one of Greg's many comics in Rodrick Rules. She was once Greg Heffley's crush, and he tried to do everything to make her notice him, until it failed when she mistakenly called him Fregley, which Greg took as an insult. Later, while signing the yearbooks, she writes a note to Greg saying that "He's Ok". She had a slumber party in this book.

She likes Rowley Jefferson, because she thinks that he is "cute" and prefers his silliness over Greg's flirting. This is true since she wrote a note in Rowley's yearbook saying that he's funny and cute. Greg, however, attempts to break this by writing a note to Holly, but what it has caused to her remains unknown so far.

Dog Days
She does not make an appearance in this book, but is mentioned by Greg when he sees her sister Heather Hills It appears that her sister works as a lifeguard at the Town Pool.

The Ugly Truth
She is never mentioned in this book, but when Greg shows online pictures of people, two of the pictures looks like pictures of Holly Hills' slumber party from book three, then when they do the egg parenting assigement & the Lock-In, a girl that looks exactley like Holly appears.

Greg Heffley
Their relationship is currently unknown, but Holly thinks that he's "OK."

Rowley
It is revealed that Holly has a crush on Rowley, and thinks that he's funny and cute, and even wants to have the same homeroom as him. It is unknown weither or not Rowley likes her back.

Heather Hills
Her relationship with Heather is unknown, since they never appear in the same book.

Trivia

 * In the online version, she is called "Piper Matthews" and is in a relationship, whereas in the the books, this isn't shown.
 * Also, whenever her sister (Heather Hills) makes an appearance, Holly appears in the next book, except for The Ugly Truth. (it is unsure if it really was Holly in those pictures)