Hi, welcome to the forum from Louisiana. Glad you joined.
A little information here could really help a lot. What has happened and what does housing look like? Did she hatch with the flock or was she separated for incubation and hatch? Have the chicks been with the flock at all or are they separated? How big in feet or meters are any coops or shelters you are using? How big are any runs or do they free range? How do any coops, shelters, or runs tie together? A few photos could really help.
What happens to the chicks when another hen chases the broody hen away? Do they get chased or are they ignored? Where do the broody and the chicks sleep at night, with the rest of the flock or somewhere else. What kind of nighttime temperatures do you have? How cold does it get?
I've had two different broody hens wean their chicks at three weeks old, left them totally on their own to make their way with the flock. The same age as yours. Those chicks managed fine. But those broody hens hatched with the flock and raised their chicks with the flock. They spent three weeks teaching the other hens to leave the babies alone. The weather was warm, it was not a factor. They had a big coop and over 3,000 square feet, over 280 square meters, of room outside. I don't know if your situation is anything like that.
If you can tell us what has happened and what you have to work with we may be able to help. Without that kind of information I can't help you.
