Abby Mallard is a female duck (implied swan) with buckteeth, wearing a purple shirt and two hairbands, which hold up her hair. A slight speech impediment and a long, asymmetrical face earned her an unfortunate nickname from the less polite kids at her school. She is accustomed to being teased for her appearance, and takes a generally optimistic approach to life. She is Chicken Little's best friend and harbors a secret crush on him.
She was first seen in class, making her teacher jump by her voice and appearance right after Foxy Loxy fakely cough out the words "ugly ducking." Later, she was at the gym talking to Chicken Little while playing Dodgeball. Little said that he had a plan, Abby thinks that closure, where one has a conversation about feelings, would be more helpful especially when it comes to Little's dad. But despite trying to convince him with magazines and trying to get Runt and Fish to agree, Chicken Little decides to stick to his plan.
When Chicken Little joins the baseball team, Abby, along with Runt and Fish, helps him train for the games. On the day the Acorns team goes against the Peanuts, Abby was seemly in charge of putting up scores and cheers along with everyone else for Chicken Little's success. Abby, Runt, and Fish, were celebrating at her house when Chicken Little called her about the "piece of the sky." Abby, when she learned that Little didn't tell his dad about it, tells him again to use closure to deal with the problem. When Fish was taken the object, Abby and the others follow Fish's glowstick to the baseball field where they saw that the object was just a part of an alien spaceship.
They went inside the ship to get Fish and, while there, saw a map of the solar system where most of the planets were crossed out and Earth was circled. Believing that the aliens were planing an invasion, the gang ran out of the ship and ended up being chased the aliens themselves. Abby suggested to rang the school bell to alert Acorn Oaks about the aliens, but while Little was ringing the bell, the aliens dislike the bell's ring and flies off into space before the citizens can see them. The citizens believed that Chicken Little has gone crazy again and Little's father was embarrassed.
The next day, Abby tells Little to try to talk to his dad, but Little thinks it's too late. While Abby was walking away with Runt and Fish, they hear Little's scream and came to see what's going on only to find a little alien with him. While learning that the alien's name is Kirby and that he was left behind from his parents, the sky appeared to be cracking and it's revealed to be alien spaceships attacking the town. Chicken Little ran after Kirby while he was running around dangerous streets. Abby soon found Little and his dad arguing and tell them that they should stop messing around and deal with the problem. Even though Abby really meant the invasion, Chicken Little and his dad had a closure conversation which did help them understand each other and Buck decides to help his son. Little and Buck sets off to help Kirby, but Little quickly ran back to Abby and kiss her before proceeding the mission. Abby was enchanted by the kiss, even while helping Runt with the firetruck to get Little and his dad into the City Hall.
The misunderstanding was eventually solved between the alien and the citizens of Acorn Oaks. A year later, a star trek version of Chicken Little's adventure was in the theater. Abby and Little was there watching the movie and enjoying the popcorn. When their hands touched, they pulled themselves back, look away and blush; but then they close in on each other and hold each other's hands.
- Abby bears a slight resemblance to Gosalyn Mallard. Both wear the same colored t-shirt and both have pig tails. They both even share the same last name. Her middle name, Ducktail, is a pun on the Disney cartoon show DuckTales.