I have had several runts, some thrived while a few didn't. My favorite was a little Ameraucana pullet who never got more than 2/3 the size of her siblings. She was friendly, which is unusual because the rest are somewhat skittish, and she loved to be picked up, carried, scratched under her wings. She never laid an egg and she never made "normal" chicken noises- her vocalizations were more like the croak of a raven but more high pitched. Her biggest shortcoming was that she never responded to any of the rooster's warnings and, one day, a hawk dropped on her like a brick.
I currently have another runt; at 3 weeks, it's half the size of its hatchmates and still has no visible tail feathers, and no body feathers- still in down- while the other 9 have full wings, full body feathering and little badminton birdy-looking tail feathers. It eats and drinks well but just has no size.
I hope it's a pullet and I hope she's friendly.