“Amy was Sophie's opposite in every way, from her curly brown hair and green eyes to her lower than average grades and incredible popularity.”
—Narration, in Keeper of the Lost Cities
She is given the name Natalie Freeman after Elvin Washers erased her memories, but her original name is Amy. When she found out she has two names, she decides to use the name Amy (meaning "beloved") because her parents were the ones who gave it to her, not a random elf that changed her memories. In the human world, however, she must continue to use Natalie in order to avoid triggering her parents' memories.
In the first book, Amy is described to be a loud, annoying younger sister to Sophie, often calling her by disliked nicknames and teasing her. Sophie considers Amy her exact opposite, with low grades and immense popularity among her friends.
When Amy is reintroduced in Nightfall, she shows much more maturity, determination, positivism, and a strong desire to help Sophie. She is extremely loyal to her family and does hours of research in order to find information on their whereabouts, although she is unable to help Sophie with any missions.
Sophie frequently checks on her, as well as the rest of her family, with an illegal Spyball, given to her by the Black Swan in the first book. At the end of Lodestar, it is found that the Neverseen attacked and kidnapped Sophie's human family. Sophie, Keefe, and Fitz searched the house and found a terrified Natalie (Amy) hiding. Amy remembers her when she sees her and calls out "Sophie?"
It is shown that Amy knows how to make her mind silent because she overhears the Neverseen talk about listening for thoughts and is able to stay undetected. Many fans believed that this was proof that she was an elf, and several guessed that she might be a product of the Lodestar Initiative. In Nightfall, however, Amy gets her memories of Sophie back and is revealed to be only human, but is very helpful even when told to stay out of the situation regarding her parents.
In Legacy, one of Sophie's memories is revealed where Sophie accidentally inflicts on Amy.
- Emma Iris Foster (Mother)
Emma Iris Foster is Amy's mother. Her name was changed to Kate Freeman when the Washers came to erase memories of Sophie. Amy is shown to love her, as she was very worried about her when she was kidnapped by the Neverseen.
- William David Foster (Father)
William David Foster is Amy's father. His name was changed to Connor Freeman for the same reason as above. Amy is shown to love him, as she was extremely worried about him when he was kidnapped by the Neverseen.
- Sophie Elizabeth Foster (sister)
Sophie is Amy's sister. Sophie lived with Amy until Fitz came to take her to the Elvin world. Sophie and Amy teased each other a lot during Sophie's 12 years in the human world (forbidden cities). Sophie is known to have stolen and hidden Amy's karaoke machine while she was living in the human world.
- Quinlin Sonden (former guardian)
- Livvy Sonden / Physic (former guardian)
Livvy likes Amy and gives her candy.
When taken to the Lost Cities, she begs the elves to let her take her two pets.