We might be right on that border or we may be one day late on it. I’d hate for her to abandon nearly fully developed chicks in the egg but we have no sort of incubator set up. I’m only letting the flock grow bc we had a broody to do it for us naturally.
To avoid this, you can mark the original eggs. (Or if you can’t tell the originals from the 3 new ones, mark those too and keep your fingers crossed they hatch.) Then from that point on, every day remove any new eggs that are added to the nest.
This is important because the other hens will continue adding to the nest until there are too many eggs for the broody to cover. Then as she rotates the eggs, the viable ones you want to hatch will get pushed out and become cold. The newer ones will start to incubate and then they too will get rotated around to the cold spots. You will end up with no eggs hatching at all.
An even better idea is to isolate the broody hen’s nest so no other hens can interfere with her. This will pay off when the chicks start to hatch. The other hens will kill the chicks. The broody can’t defend them when she is still sitting on the remaining eggs, so the first ones to hatch wander away from her and get eaten as though they were a mouse. Perfectly natural behavior for chickens.
But if the broody has a wired off area around her nest, she can have a few days to bond with the chicks and teach them to obey her when she signals for them to come and hide underneath her. Then when you open up her wired area, she will teach those other hens in no uncertain terms that her chicks are off limits!
It is a beautiful thing to watch a hen raise chicks. If your rooster has the right personality, he will help her. That is really nice to watch as well.
Also, if possible, see if you can find another chicken keeper nearby who has an incubator you can borrow for backup, or who could take any unhatched but still viable eggs when the broody does get off the nest. I haven’t done this with chicken hens. Mine don’t seem to leave viable eggs in the nest. But I have saved a few goslings and turkey poults when their clueless mothers botched hatch day. I was able to put the leftover eggs into the incubator and get some to hatch.
Good luck!