Ewh, that's a tough one. If it's a first time mum I'd put the chick in the brooder box. If she's an experienced hen I'd let her take care of the chick. At least she'd have the joy of her one chick. It would be good to keep the Rooster away for a while just in case. Sad that the other five didn't make it. Keep me posted!
Leave her with mom...mom can do it better than you ever can. That chick will stay at the correct temp with Mama while she waits for other eggs to hatch. They can live on their yolk for a few days during the wait.