Broody hen

Don't leave her there. Her health will deteriorate.
Put her in a dog crate with a wire bottom and put the crate up off the ground so cool air can blow across her belly. Keep fresh water and food in the crate with her. You may also want to direct a fan up under her to help cool her down.
Keep her in the crate for the day then let her out in the evening about 2 hours before normal roost time to run around and dust bathe. If she goes back to the nest after that, immediately put her back in the crate for the night.
Let her out again in the morning for a stretch and to eat. As soon as she heads back to the nest, into the crate she goes. You get the picture.
I broke one broody with 3 nights and one day in the crate.
My second one would not break after nearly a week in the crate and cold water belly soaks. She is now sitting on 4 fertile eggs... be warned. Some are VERY stubborn.

 

A hen will, if undisturbed, remain broody until the 21-day incubation period ends, or until an egg hatches underneath her. The latter means that a hen can stay broody for a month or more, until she hatches something.
There are several ways to break a broody, from placing a bag of frozen vegetables underneath her to sticking her in a cage that is suspended above the floor and has no bedding. The aim is to cool off her underside, as she'll realize that she can't incubate if she isn't warm and will break out of her broody mindset.
When one of my hens, Najika, went broody, I let her sit on a guinea egg until it hatched, and when she still remained porcupine-esque, I put her on the perches at night and closed the door during the day when they were all outside and I had removed her from the box.
Looking up "how to break a broody hen" should supply you with several methods of breaking your broody hen.
Good luck, and I hope that this helps.

 

If you don't want her to hatch out chicks, best to break her broodiness promptly.

My experience goes about like this: After her setting for 3 days and nights in the nest (or as soon as I know they are broody), I put her in a wire dog crate (24"L x 18"W x 21"H) with smaller wire on the bottom but no bedding, set up on a couple of 4x4's right in the coop or run with feed and water.

I used to let them out a couple times a day, but now just once a day in the evening(you don't have to) and she would go out into the run, drop a huge turd, race around running, take a vigorous dust bath then head back to the nest... at which point I put her back in the crate. Each time her outings would lengthen a bit, eating, drinking and scratching more and on the 3rd afternoon she stayed out of the nest and went to roost that evening...event over, back to normal tho she didn't lay for another week or two. Or take her out of crate daily very near roosting time(30-60 mins) if she goes to roost great, if she goes to nest put her back in crate.

Chunk of 2x4 for a 'roost' was added to crate floor after pic was taken.