I don't know how big she is... but for a first time mom anywhere from 3-5 more. It really depends on what you want to add to your flock and what you plan for them. There is a slim chance she will object to them also, though I would still try! Just have a brooder set up as a back up in case you need it (or at least the equipment on hand to set one up quickly if you need to)
Above 25 degrees I wouldn't bother with the heat light unless she was compromised somehow (heavy molting, low body weight, etc.). Make sure she has plenty of fresh bedding (straw or wood shavings) both under and around her. Just make sure her water doesn't freeze or you refresh it frequently so it is available on the infrequent times she gets off of the nest.
I think I have the incubator stable enough and could just put all 24 in it but I wanted to try both ways.
Decide how many you want to raise, or have her raise... since it's her first time I'd keep it on the lower side to make it easier. Your little lonely one will be happy with any brothers/sisters. I would go with at least 3 just to make sure there is no problem with losses.
That is one reason why lots of people isolate their broodies, so they won't switch nests. It could be that she was forced out or left her nest for a reason and when she returned it might have been taken already. Does she have false eggs under her? Usually with ping pong balls under my broody I can extend the stay for at least two weeks until I get fertile eggs under her. If not, she could be ready to give up being broody. You could give her a few and put the others in the bator then when is hatch time let her finish the hatching.Well I'm picking up my eggs tomorrow so I went to check on my broody hen and to give her some tuna. I came back out an hour later and she was in a different nest box than the one she has been sitting in for three weeks!
Now I have doubts sticking eggs under her.
