She should stay on the nest for a day or two after the first one hatches. Some broodies will attack their chicks, so that's the main concern with a novice hen when the eggs start to hatch.I work from 5am to 4pm every day. Will it cause problems if one hatches while Im at work? I dont have anyone at home for those hours for 2 days. im very concerned she will leave the nest after 2 or 3 hatch!
Occasionally an adventurous chick will wander off too, and chill or get attacked by other chickens, so having them well confined will help avoid that.