Relax, it sounds like it is going the way it is supposed to.
Before a hen even starts laying eggs she builds up excess fat. That fat is what she mostly lives off of if she goes broody. That way she can take care of her eggs instead of having to be out looking for food.
A broody hen should leave her nest occasionally to eat, drink, poop, and maybe take a dust bath. She does that on her schedule, not yours. I've had a broody hen leave her nest twice a day and stay off for over an hour each time. I had a broody leave her nest once a day and for only 15 minutes. Several I never see off of the nest but I know they are coming off because she is not pooping in her nest. Trust your broody, they have been doing this by instinct for thousands of years without help from us.
If you want to take her off of the nest you can. It will not hurt anything. When I set them on the coop floor they tend to set there for a few or even several seconds, just flattened on the floor. Then they either get up and go eat, drink, poop, and such or they immediately go back to the nest. As long as she is not pooping in the nest she is getting up, but on her schedule.