I strongly agree with Won Sunshine, I too am a believer in keeping the hen & chicks with the flock. Mine are separated only a bit more than 24 hours.
When you separate the hen & chicks away from the flock, the hen loses her pecking order. When you reintroduce the hen and the chicks are older, her hormones are falling as she is getting over being a broody hen, her urge to protect them is deminishing, and she has to fight for her own pecking order.
If you have the hen with the flock the entire time, everyone (even the roo) kind of tiptoes around the broody hen. She is quite high on the pecking order. She is given a rather wide berth when she brings the chicks out. And she defends those babies harshly.
Mine right now, are 3 weeks old, and I saw several in the food bowl, right with the layers this morning. They didn't stay there long, but they were pretty tolerated, and not pecked viciously. Once I lost a broody hen and most of her chicks, 4 escaped, and came back to the coop at night. They were only 4 weeks old, and if I tried to introduce 4 week old chicks to an established flock of layers that would be a nightmare. However, they were all used to each other, and never had a problem.
Once you go broody, you never go brooder...... if you can help it at all!
Being you have kept them separated, you do need to watch closely and see how it goes, but I agree with Walking on Sunshine, sooner is better.
I also agree, not all animals make good mothers, or mother the same way. We have cattle, and some give their calves a lick and a promise, and move that calf 5 miles by morning. Others, I think are going to lick the hair right off the calf. Just like people, some are good mothers, and some are not. If you have a hen that is not a good mother, don't let her do it, in fact I would not keep her in my flock.
Mrs K