Make an extra roomy nestbox for her to brood in. Put it in a quiet corner but where she can get out to eat and drink but in eyeshot of her box.
The other hens and rooster would troop by once or twice a day to check on her progress. Hens added a couple more eggs when I wasn't looking. Be sure to mark the eggs you set under her, so you can pull the ones added after she starts brooding them. Start all the eggs at the same time so they hatch all over two days. the hen will gather the chicks up and leave the nest box. Have another place for them ready.
One other thing - it took longer than 21 days so don't give up till about 26 days. Towards the last week, the broody would leave the nest in the afternoon for about two hours and I thought it wasn't working so on day 23 so I started tossing out the eggs - my mistake, live chick still not finished developing! So I put the rest of the eggs back and they all hatched fine healthy chicks. Easter Egger and Brahma/Easter Egger crosses. It was warm in the afternoons about 80 degrees so I guess it didn't hurt.
One thing that helped my broody - I hung the box off the floor with wire to keep the mites out and mongooses. No wood touching the floor for mites to climb. The floor was six feet off the ground, but there was this long line of mites coming up from the ground, up the posts, across the floor and up into the nest box. I was in Hawaii, where you are might not matter. Could put diatomaceous earth all over the bottom of box to kill mites. Still some mites were on the hen, and they would attack the chicks eyes while they were hatching and still in the egg.
When the chicks hatched, I put them and the hen in a 4 x 8 tractor on the lawn. It was so cute seeing them peek out from under her and over her wings. I took them food and water every day, and slid the tractor over to new grass. When they feathered out fully, one day the hen wouldn't let them near her anymore, so I turned out the hen, but let the chicks get bigger in the tractor before I let them out.
Have fun. It was the best ever seeing the cute chicks peeking out from under the hen.