You have a few options. You can isolate the broody, either block off that nest so the others can’t get to her or move the broody to another location. If you do that, she will need her own food, water, and some room to go poop, though you may be cleaning the food or water out. Broody hens know to not go poop in the nest but they don’t know not to go poop in food or water. You’ll have to keep her locked up so she can’t go back to her old nest or she will abandon the eggs and go to her old nest.
Your other option is to mark the eggs you want her to hatch and check under her every day to remove the unmarked eggs. I use a black Sharpie and make a couple of circles around the eggs, one the short way and one the long, so I can tell at a glance which ones belong. As long as you remove the eggs daily they are good to use. You won’t find any surprises in them. Also, if the number of eggs build up to where the hen cannot cover them all, some will cool off and die, get moved back under her, and others get shoved out, cool off, and die. It’s important that the hen can cover all the eggs.
It’s important that the eggs all start at the same time. Collect all the eggs you want her to hatch and set those. If they start at different days some will hatch earlier than others and she will abandon the unhatched eggs when the first ones to hatch need to go get food and water.
There are risks either way. If you isolate her you obviously have to work harder feeding, watering, and cleaning. She may not accept the move and break from being broody. It needs to be someplace predator proof and safe from overheating this time of year. Some other bad things can happen but those can happen whether you isolate her or not.
If you don’t isolate her you do need to check under her daily. It’s possible she may find another hen on her nest laying when she returns from her daily constitutional, get confused, and go to the wrong nest. I’ve had that happen where the eggs were really cold to the touch but I just put the hen back on them and she hatched 11 out of 11. Still, that is not a good thing to happen. The other bad thing was when a second hen went broody and the two fought over the eggs. That was about the time the eggs started internal pip so the hens could hear the chicks inside the eggs. They destroyed some eggs during that fight.
I still allow a hen to hatch with the flock. These bad things are fairly rare but they do happen, especially the hen going to the wrong nest. It’s the way people have been keeping chickens for thousands of years and just seems more natural to me, but it comes down to personal preference. There is nothing wrong with isolating a hen either.