X2 with Amy, she sounds like she just likes the nest box to sleep in. This is a bad habit you should really get your hen out of doing. It can be quite unhealthy for them to pooping right where they are sitting. They should ideally be on a roost so poop can fall away from them. Pooping in the nest box can make for dirty eggs. If I have a nest box sleeper I remove the hen and put her on the roost and block the nest box off do she can't get in anymore. Popping out then about an hour before bed to block it off for a few days usually does the trick. Here is an article for you to check out on broody hens > https://www.backyardchickens.com/a/broody-hens
I agree with amylynn2374 and Yorkshire coop in that it does not sound like normal broody behaviour.
Has she slept on the roost in the past?
If she has, I wonder if anything has changed which has caused her to feel more comfortable on the floor in a nest.
Maybe one of the other hens is picking on her or there is now not enough room for her on the roost.
Sometimes chickens are reluctant to roost if there are red fowl mite biting them during the night. Red fowl mite tend to hide in the cracks and crevices of the coop and roost and come out at night and feed on the chickens.
If she has never slept on the roost, it does sound like she has just got into a habit of sleeping on the nest.
As Yorkshire coop suggested, I have had a nest box sleeper and blocking off the nest box in the afternoon has cured her of the habit.
Also, if she has never slept on the roost, I wonder if she is able to reach the roost, is it maybe too high for her? Some breeds, Silkies etc, are not good at getting onto a high roost.
Might be an idea to not leave eggs in the nest and ensure all have been collected in the afternoon.