Harley Riley is Marc's little sister. She is like most little girls her age and is interested in very girly things, such as dolls, ponies, dresses and the color pink. She like to act very cute an innocent to get attention from other people while pestering her older brother the rest of the time. Though she likes to push Marc's buttons, she cares deeply for him and often looks up to him for guidance and protection. She is the only one out of her immediate family who knows Marc is an elf. Harley likes to follow her older brother around and often gets herself in trouble when she follows him to some place dangerous, when she knows she's not supposed to. She's a bit mischievious but is all around a good kid, despite the whining she does from time to time.
She carries with her a white, stuffed bear names Po and she will often pretend to talk to it and convey the imaginary message to other people.
- People often ask her if she is an elf due to the confusion of whether her brother was born an elf or not. He wasn't, and so she is human.