Amy has red shoulder-length hair, bright green eyes, and a thin body shape. Amy is missing her left hand and refuses to wear a prosthetic, leaving the stump-wrist exposed.
In the film, Amy has brown hair, brown eyes, and wears a prosthetic hand.
Amy was sheltered as a kid and teenager, which caused her to be very unexperienced at taking care of herself and afraid of the outside world. She has a cute, likeable personality and is very intelligent. In spite of her inexperience in life and her disability, Amy is very capable and accomplishes everything she sets out to do. Amy nearly always gets her way because of her determined way of thinking. Amy is very kind, loving, and understanding. She is also very emotional, and can have problems controlling her feelings. She is still able to contain herself when necessary, though. Because of Amy's sheltered childhood, she is slightly socially awkward and sometimes speaks her thoughts out loud. This causes her to say strange and sometimes inappropriate things without meaning to, leading many people to believe she is mentally disabled.
Amy grew up in an overly religious family with her brother Jim. In her early teens, Amy was involved in a car accident that severed her hand and killed her parents. Several attempts were made to reattatch her hand, but the damage was too large and her hand was eventually amputated (without her consent). She was forced to take pain medication, all of which gave her awful side effects. Amy became depressed after losing her hand and taking the medication and was transferred to a special education school for her remaining years in high school. This is where she met Dave the first time, though they never spoke to each other. Amy met Dave again when her dog, Molly, went missing and Dave returned her. She told him to keep Molly and they did not speak to each other again for several years.
Amy's brother died soon after the disappearance of Molly. She had to learn to care for herself without the help of her parents, brother, or dog. Strange things began happening to her at age 19. She was losing time; she would be going about her daily life, blink, and it would suddenly be several hours later. During one episode, she lost twenty hours. She mysteriously disappeared for those hours, and John and Dave were recruited to find her. While she was gone, a large floating jellyfish with a sexual attraction to lamp fixtures appeared in her basement. Also, a 40 pound plastic bag of fat randomly appeared in her house. When she came back to Earth, she popped back up in her bathroom with no recollection of the past 20 hours. The jellyfish and bag were nowhere to be seen.
She encountered Dave for the third time when he kicked down her bathroom door after she reappeared in her house. She was initially frightened, not knowing why she couldn't remember the past day and not knowing why Dave was in her home. She agreed to let Dave spend the night after they came to an understanding of the current situation and begins to show an interest in him. She was then reunited with Molly. That night, Amy loses time again, and disappears for several hours. Niether Amy nor Dave can remember what happened during the hours she was gone.
The two hide out in Dave's car after they are chased by the Shadow People. Dave warns her that she is in danger. He gives her a gun, shows her how to use it, and says to shoot him if he tries to hurt her. He tells her about his past, and about bad things he has done, but she does not believe he is a bad person. Instead, she feels safe with him.
When they are able to leave his car, they retreat to Dave's house. It is then she realizes that Dave has feelings for her. It is implied they sleep together. A series of events lead them to figure out that Amy had been slipping through dimensions during her lost time and a group of inter-dimensional beings were experimenting on her. After the problem is solved, she moves in with Dave and attempts to start a relationship with him. He believes his lifestyle is too dangerous for Amy and convinces her to leave. She complies, but still calls him every day. Eventually she decides to move back and attends college in a town near Undisclosed and becomes engaged to Dave.
At the end of TBIFOS, it is revealed that Amy's hand was not lost in the car accident, but it was in fact taken by the Shadow People.
Even though she has never taken the Soy Sauce, Amy still has some supernatural abilities. She can see things most people cannot see without taking the Sauce. This ability has been explained as the Soy Sauce entering her body in controlled amounts during a "transfer of body fluids" caused by intimate time with Dave. In addition to seeing things other people cannot see, Amy can touch them as well. This is explained by the ghost of her hand occupying the space where her physical hand should be, and the ghost of her hand is able to touch and manipulate objects that are invisible to the naked eye.