|“||I can't even qualify for the Olympics until I'm sixteen!||”|
–Kayla worrying about her archery skills after Apollo becomes mortal in The Hidden Oracle.
Kayla is among the campers that go to New York City and fight for the Olympians. She and her half-brother, Austin, set traps along the Brooklyn Bridge with their half-brother, Michael Yew, directing them.
Kayla survives the battle and is commanded by the new cabin counselor, Will Solace, to look for Michael Yew. Michael's body is never found (though he is later revealed to have died), as this seems to be the general opinion at the memorial ceremony. Percy Jackson only sees his bow and presumes that he had fallen into the river below the Williamsburg Bridge.
Kayla, along with Austin, visit Apollo when he is brought to Camp Half-Blood. After learning that their father became a mortal, Kayla worries if the skills and powers they'd inherited from him are going to disappear. She then asks if they themselves are going to be un-born, her father assures her that it would not happen.
The next day she tells Apollo to keep practicing and his archery skills will improve. She was shocked when he swore on the Styx to not play music or practice archery until he was a god again. They stopped Sherman Yang from going into the forest.
Apollo mentioned that Kayla told him to maintain his equipment while traveling. When her immortal father is aiming for the lever on the train tracks, he remembers how she had encouraged him what she had told him about patience.
After escaping the Strixes, Apollo wonders how Kayla is doing at camp.
When his father and Meg return to camp after six months, Kayla and Austin argue with the harpies about eating new campers on their third warning rather then the first. The following morning she greets her immortal father after returning from a hike and tells him she wants to help take out Nero during breakfast.
A couple of days later the camp mounts an attack on Nero's Tower. As she is fighting, Nico hands her immortal father over to her and she patches him up and gives him Mountain Dew. She walks him to a dining room where campers are being chased by a Tauri Sylvestres and she passes Apollo over the Austin so she could help them. After the battle is over, she and Austin help with the wounded as they give Apollo a reassuring look.
Two weeks later she and Austin hug their father when he returns to Camp Half-Blood as a god.
Kayla has short ginger hair dyed with a shock of bright green and blue bell eyes. She has freckles covering her skin.
Kayla is shown to be kind, as she tried to calm her immortal father when he was turned mortal. She is also driven, as she desires to become an Olympic archer when she is old enough.
- ADHD: Like most demigods, she has superhuman reflexes.
- Dyslexia: Her brain is hard-wired for Ancient Greek instead of modern languages.
- Archery: As Apollo's daughter, she is a naturally talented archer, her skills only rivaled by her aunt, Artemis' maiden hunters. Kayla seems to take pride in her archery skills the most.
- Musical Aptitude: Since Apollo is god of music, Kayla is a natural musician.
- She can curse others to only speak in rhyming couplets that can take days or even weeks to wear off.
- Vitakinesis: As daughter of Apollo, she can heal people by singing to her father in Ancient Greek.
- She is skilled in physical contests and games.
- Kayla means 'laurel' in Arabic, suggestive of a reference to her father since the laurel happens to be his symbol. In Greek, her name would be derived from the name Katherine, which can mean 'pure'.
- Knowles is a common surname of Cornish origin that is said to be derived from the Irish surname “Ó Tnúthghail”.
- Kayla is the only known Greek demigod with a human parent being the same sex as their godly parent.
- The way that she was born is unknown, not being known if Apollo is who was pregnant or Darren (though given his interactions with Sally Jackson when she was pregnant, it is unlikely it was Apollo, as he seemed to have trouble understanding the concept at all). It's also possible that Apollo birthed Kayla with Darren in a similar to how Athena's children are born.
- She wishes to try out for the Olympics as an archer.
- Kayla is technically the first Canadian demigod in the series to be introduced, making Frank Zhang the second Canadian demigod to appear in the series. However, Kayla was only mentioned, in The Last Olympian, making Frank the first Canadian demigod to "appear" in the series.