The Chicken of the Family by Mary Amato, illustrated by Delphine Durand

From chapters.ca:
Henriettaas two older sisters love to tease her. When they try to convince her that she is actually a chicken instead of a little girl, it's pretty hard to believe at first. But the evidence is all there: her legs are kind of yellow, and her toes are kind of long. The feathers she finds beside her bed the next morning settle it, and Henrietta heads off to the farm to find her real family. The chickens welcome her with open wings, and this lovably gullible heroin's joyful acceptance of who she really is will have readers squawking with laughter.