"Arlo’s sister Libby is a capable and willful girl who can plow a mean field. The little trickster has a great sense of humor, and loves playing silly pranks on her family."
The Good Dinosaur
Libby is the first of the three children of Poppa Henry and Momma Ida to be hatch out of her egg. Then, out comes her brothers, Buck and finally, Arlo. She spends the first day of her birth playing around the house with her parents and brothers.
Years later, Libby has grown a little older and is charged with watering the corn field until she tricks her brother, Buck, who is in charge of removing logs, into doing it for her through teasing by squirting water on him. Once Buck is done unintentionally and unknowingly finishing her chore for her by watering the field while trying to squirt back at her with barely avail, Libby tells their mother that she finished her job. Libby thanks her mother after she congratulates her and angrily tells Buck to "get back to work"; much to Buck's shock annoyance.
When Poppa Henry finishes building the corn silo to protect it from critters who might eat from it and makes his mark with his wife, Libby and her brothers try to do the same but their father reminds them that in order to make their marks, each one has to earn it by doing something big, bigger than themselves; much to Poppa Henry and especially, Arlo's eagerness.
A couple of more years go by and after Buck earns his mark by clearing a field, Libby earns hers by plowing the new open field properly. With every fear and failure, Arlo is the only left with a mark unearned. After Buck messes and teases with Arlo, Libby is present with her parents when her father scolds Buck and comes to Arlo's defense even when Arlo almost gives up.
Days after her father has been tragically killed for trying to save Arlo from certain death from a flood created by a storm when going after a critter, Libby and everyone else continues his/her own chore even before gets separated from home chasing after the critter.
Days later, after Arlo returns fearless and triumphant, Libby and everyone else welcome him back home with hugs and watch him finally make his mark on the silo.