She will remain broody until her hormones return to normal, and then with luck, she will begin another egg laying cycle. There are several factors which will help this to occur; exposure to as much light as possible, rather than the darkness of a nestbox; confinement in a bare area where there is nowhere to snuggle down and nest; and cool temperatures, i.e., below what she would encounter in a warm nestbox. The slight stress of being netted off away from the other hens, though still within sight of them, will also help.
Three ideas -
1) partition off a corner of the run and leave her out there overnight, with shelter from the rain under a box but with just bare ground underneath her, no bedding - or use a dog carrier, rabbit run etc to confine her away from the coop. Overnight, you could put the carrier in a shed or garage if it's not safe in the run itself.She will stay cooler out there, and the slight stress of separation will also help her hormones to decide that maternity isn't a good idea.
2) If you can't safely leave her out in a corner of the run overnight, try making a small enclosure with some netting in a corner for daytime use, so she doesn't get a chance to go in the coop during the day. Or, even better, if you can make a circle of chicken netting on grass, leave her outside on her own in there during the day, with pellets and water. She will complain and march around but the exercise, and particularly the exposure to light will be helpful.
3) If you feel she must roost in the coop overnight, block the nest boxes with upturned large plastic flowerpots after the hens have finished laying, so she at least has to perch and isn't tempted to snuggle down in a nestbox. You may need to go down after dark and check that she is actually perching, and not nesting on the floor. If she is doing this, lift her on to a perch. And remember to remove the pots before the hens want to go in to lay!
With experience of a particular hen, you'll notice the first signs of her broodiness and can begin treatment before she really gets stuck in. I used to have all the equipment ready for when my Buff Sussex went broody yet again, and found that she could be cured in 2-3 days if I caught it early enough. It may take much longer if she has already been broody for several days.