We went back in the night, when it was completely dark (rather than dusk as earlier) and slowly added chicks to her, just a few at a time, as advised on the downsizer forum. And no defensive fluffing up, no noise apart from the occasional cluck. Once all fifteen were under (we had to cull one that wasn’t right), we slipped away and went to bed.
She seems to have accepted them as her own.. in fact looks pretty smug about it all.. she was sitting on one (fake) egg for 2 weeks, and hatched 15 day old chicks! – yeh i’d be smug too. And of course – a reprieve for Henrietta.
By our calculations, it costs the equivalent of three sacks of layers pellets to use the heat lamp and get chicks to the point they are off the heat. So if Henrietta does that just once , we will be saving (as she doesn’t eat that much!). Besides it is a lot easier and less smelly for us, and a lot more natural for the chicks.