I don't know. I've never waited that long to let a broody raise a chick with the flock. I'm not sure how the rest of the flock will react to a strange hen and chick being introduced. I'd expect Mama to be so protective of the chick and to have such a bad attitude where protection of the chick is concerned that things would work out, but I really don't have any experience with that specific situation.
When mine hatch chicks with the flock I let them raise the chicks with the flock. Most of the time the other chickens leave the chicks alone but when a hen gets aggressive Mama quickly teaches her better manners. That's the way chickens have been raised for thousands of years. I just don't have experience reintegrating a hen and chick where the hen has been absent for at least three weeks. Even when a broody hides a nest, she stll mixes with the flock some when she is taking her daily constitutional so she is not totally forgotten.
I'd try introducing them and I'd expect you to be OK, but I sure can't give any guarantees.
