You've got one hen left, she's curled in the nesting box like a feathered crypt-keeper, and you're juggling a baby and a toddler. I see you. And I also see that mirror you propped in the coop, bless your heart, that's the kind of desperate, hopeful energy we respect around here. The question isn't really about chickens anymore. It's about how much of your very limited soul you can spare for a traumatized bird who might not even want your help.
Let's start with option B, giving her away. That's the honest, low-effort play, and there's no shame in it. You've got tiny humans who need you, and a solo hen who's basically a living stress ball. Someone with an established flock and the bandwidth to integrate her could give her a softer landing. You'd be out one chicken, but you'd also be out the guilt of watching her mope. If your goal is least work, this is the closest thing to a clean break. You'd just need to find the right person, someone who understands that she's not "friendly," she's shell-shocked.
Option C, pullets, sounds sensible on paper, but introducing even half-grown birds to a single, traumatized hen is not a quiet project. Pullets are teenagers. They're loud, they peck, they don't care that your hen is grieving. You'd be managing a pecking order while also managing a toddler who's trying to eat a slug. That's not saving energy; that's trading one kind of exhaustion for another. And if she's too freaked to come out for food, she's not ready to defend herself from new arrivals.
Option A, chicks under a broody hen, has a certain storybook charm, but you said she's been broody, and right now she's not broody, she's broken. A hen who won't leave the nesting box because she's scared is not the same as a hen who won't leave the nesting box because she's ready to hatch. Pushing chicks under her could go one of two ways: she snaps into mama mode, or she ignores them and you end up with dead chicks and a worse mess. With a baby and a toddler in the house, you don't have the margin for that gamble.
You're not a bad chicken parent if you rehome her. You're a tired one. And the kindest thing you can do for that hen, and for yourself, is to find her a place where someone has the time to coax her out of that box without also having to unstick a Goldfish cracker from their hair. Give her away. Then take a nap. You've earned it.