Two practical bits nobody mentions until you have been through it.
Check her over while she is off the nest. A hen sitting for a week and a half in warm weather is a good host for mites, because she is stationary and not dust bathing. Have a look at the vent and under the wings, and at the perch ends after dark. It is the sort of thing you find by accident at exactly this moment and it changes what you do next.
Sort out where the other three are laying now. They have moved because the box is occupied, and once a hen starts laying in a hedge she often keeps doing it after the box is free. Shut them in the run for a couple of mornings once the broody is broken - most hens lay before midday, so you only need to contain them for half a day to reset the habit. Otherwise you are hunting eggs in the garden until autumn.