If she isn't showing any interest in the chicks, I would suggest putting her back with the rest of the flock. You should be able to just put her straight back, they might have a little tiff as they sort out pecking order again, but other than that they should be fine.
If she has gone back to laying eggs and has pretty much abandoned her babies, I doubt she would be desperate after separating them from her. She could start to attack the babies if she's really decided she's done with them.
Same with the orphaned chick, there might be a couple of pecks on the head when you introduce it to his/her siblings, but chickens sort themselves out in the end. As the momma has rejected that specific baby, I wouldn't introduce the chick to the others until you have made the decision to separate the hen.
As for the broody questions, I don't really have an answer. All I can say is that a hen decides when/if she wants to go broody, and either way, it's pretty hard to change her mind
If she has gone back to laying eggs and has pretty much abandoned her babies, I doubt she would be desperate after separating them from her. She could start to attack the babies if she's really decided she's done with them.
Same with the orphaned chick, there might be a couple of pecks on the head when you introduce it to his/her siblings, but chickens sort themselves out in the end. As the momma has rejected that specific baby, I wouldn't introduce the chick to the others until you have made the decision to separate the hen.
As for the broody questions, I don't really have an answer. All I can say is that a hen decides when/if she wants to go broody, and either way, it's pretty hard to change her mind
