If it were me, I would just make sure it has plenty of food. Skunks are among the least aggressive of wild animals, simply because their spray makes them formidable without ever having to fight. They are by nature mellow and calm, and if it thinks that hen is its mother (and she doesn't mind!) I think it can work out. Skunks and chickens have similar diets, so she can even teach it to look for food. I would just make sure it never gets hungry so it never even thinks about chickens being made out of meat. I have heard many tales of wild adult skunks burrowing under coops to eat chickens, but perhaps a resident skunk will deter them. Look into how territorial skunks are... that is an important thing to consider. If it will draw other skunks during mating season, that might be a problem, even if it is a good pet.
I have read stories of bears, gorillas, and ferrets with kittens. People raising lions that recognized them years after release into the wild. Of great danes with lions and deer. Even a tortoise with a hippo! Some animals just have so much parenting instinct that they cannot turn away a baby in need. And you know what? In every one of those stories the baby was a faithful companion of that older animal as long as they both lived. I say you are lucky to have such a unique relationship in your family. That little one will learn a lot from its new mommy and I bet that it wouldn't dream of trying to eat her. Even if it did think of snacking on her babies when they hatch, it would only get one nip in before she set it straight and it would never try it again.
Good luck!