I don’t think you can expect a broody to be ripped out of her environment and put her in a brand new situation with already hatched chicks and expect her to go right into mothering them. It is extremely stressful for her to have that much change and just because a hen likes sitting on eggs doesn’t mean that she’ll be a good mother - as you just found out with your hen. This big change is very likely to snap her right out of her broodiness. And what will happen to her afterwards? You shouldn’t integrate just a single hen into your flock. Plus what about quarantine for a new flock member??
The thing to do is to make a quick brooder and raise them yourself!
The thing to do is to make a quick brooder and raise them yourself!