If you can, I think it's better to separate the broody from the rest of the flock. Otherwise, other hens could add eggs to her nest after she's started to incubate and then they won't hatch at the same time. Sometimes another hen will bully a broody off her nest and the eggs chill before she gets back to setting. This happened to the clutch that our head hen, Billina came from. She was the only chick to hatch out of that clutch.
If you can't separate the broody, be sure to mark the eggs she's started to incubate so you can remove any other ones that get added.
I think it's also safer, if possible, to let the broody raise her chicks in a separate pen. Other hens will sometimes attack chicks, and although the broody will usually defend her chicks she can't be everywhere at all times.
Certainly let the broody raise her chicks. It's easier for you, and she does a much better job than an artificial brooder.