Andrea was born sometime in 1993 or 1994 to William and Sharon Harris. She lived a normal life with her parents in Atlanta, Georgia, not knowing William was a psychopathic rapist. Eventually, her father was charged with the rape and abduction of two women, but the charges were dropped after the victims refused to testify. In July 2008, William moved the family to Sarasota, Florida, under the pretense that the stigma placed on him and his family had become too much pressure. Andrea apparently moved on from the events, settling into the community and her new school nicely. All the while, she never knew that William had escalated to raping and killing local teenage girls alongside a newfound partner.
Andrea is first seen being given a driving lesson by William. Before she could even turn on the car, William is interrupted by a page, and he tells her that he has to go. Andrea is upset, since he had been postponing their driving lessons repeatedly, but William reassures her by stating that he plans on giving her the car as soon as she gets her license. As they exit and embrace, one of Andrea's new friends, Lisa, arrives, and Andrea boasts to her that she already has a new car. Then, another neighborhood girl approaches, showing them a "missing" poster featuring the photo of a girl named Missy DeWald, who goes to the same high school as Andrea and Lisa. This alarms them, as the killer's victims have been getting younger and he is alternating between African-American and Caucasian girls. Shortly after, local police, led by Detective Linden, pull up and arrest William in front of Andrea, Sharon, and several neighbors, for the abductions of Missy and the murder of three other teenage girls.
Andrea is later present as police search her house, with neighbors looking at her suspiciously. She is then interrogated by Hotch and Prentiss, who ask about William's whereabouts for the last 24 hours. Andrea replies that he had been home with them, though Sharon adds that he may have been out of the house for about an hour or so. Hotch and Prentiss then ask about why they moved to Sarasota six months ago and bring up William's rape charges in Atlanta, but both Andrea and Sharon assert it was a mistake. The two agents then attempt to ask about William's relationship with his family as of recent, but Sharon has had enough and forces them to leave the house. Later, Andrea and Sharon visit William as he is being taken to jail, and he tells Andrea to take care of her mother and be strong in the meantime. He then convinces Sharon to pay for his $5 million bail by selling the house. Though Sharon agrees to do it, she is visibly shocked by her husband's proposal and begins to doubt him.
Later, after the BAU suspect William of operating with a partner, Prentiss interrogates Andrea, asking her if there are any locals William may have either gotten close to or is taking extra precautions to avoid. When she profiles the partner as someone similar to William, Andrea accuses her of now pinning someone else's father for the murders, but Prentiss assures her that is the last thing on her mind. Prentiss then says that the partner is someone Andrea would recognize, and someone who is likely to check up on the Harris family, as he is worried about William but cannot communicate with him, so he would have to communicate with Andrea and Sharon instead. Andrea then tells Prentiss that Sarasota is nice, but after what has just happened, it will be like Atlanta: everyone will assume her father is guilty, and it will get worse from there. Later, Andrea's new car is egged and spray-painted. The Harris family is consoled by Steven Baleman, one of their new neighbors. Andrea becomes suspicious of Steven, but her mother defends him, saying that he is the only one on the block that has been helpful while William was in custody.
Andrea later goes outside and sees what the vandals had done to her car. She is then confronted by a group of classmates, who taunt her about her father and inform her that they learned about the dropped Atlanta charges in the newspapers. One of the teens tauntingly suggests that William may have first started out raping Andrea. Before Andrea could assault her, Steven intervenes and orders the teens to leave, which they do. Steven then tells her that he is around if she needs company, which unsettles her, but she kindly turns down the offer. Later, Andrea overhears an argument between Steven and his wife Annie, and notices him leaving. Remembering Prentiss mentioning to her that the partner would be experiencing mood swings as a result of William's arrest, Andrea secretly follows him to a local warehouse by the harbor. There, he notices she is following her and abducts her. Hours later, William suddenly appears and frees Andrea, at which point Steven confronts them and asks William about his betrayal. William denies it and asks Steven why he had taken Andrea, telling him that their family members were always off-limits and mentioning Steven being responsible for Missy's murder. The BAU and local police then show up and arrest both William and Steven, with Andrea breaking down in tears. She is later reunited with Sharon, and tells her she wants to "go away".