Be careful Jillyc, we had a hen had 2 chicks and only a couple of hours later another hen who had had chicks a few hours before died (possibly dehydrated). I put the dead hens chicks with the other mum and her 2 and watched her for about half an hour - no problems, seemed to treat them like her own - went back an hour later and she had killed both. If she's not sitting on her nest any more and you stick them under her she may be wise to it. Think it would be better at night and she might forget overnight how many she has and be fine with it, but you will run the risk of the chicks being killed (it's a food competition thing as to why they kill them). Tricky situation, good luck. Let us know how you get on.