It very much depends on the bird, but generally Broody Hens do not get up often. My first Broody only got up once every 3 days to poop, and she only ate and drank once a day, very early in the mornings before I visited the coop. In the whole 21 days, I only saw her off the nest twice, but her food was always nice and neat in the evening, and messed up in the mornings, so I knew what she was up to!
Broody #2 is currently on her nest of 10 eggs for 7 Days now (candling soon, woo hoo!) I have not seen her off the nest yet, but yesterday she turned around when she was alone so that when I went into the coop she was facing in the opposite direction on her nest! I think she did this so she could see our first Broody's chick when he came out to play.
I am a little confused about your post "Sometimes there are eggs under your broody." Whose eggs are they? Obviously if she is sitting she will have whatever you gave her to start with. Are other birds laying in her nest? If so, you really want to separate her from the others. A staggered hatch is not a good idea, as your hen will normally leave the nest after 24-36 hours with whatever chicks have already hatched, often leaving completely viable, yet younger eggs, unhatched in the nest.
If she is still laying it would suggest to me that she thinks she doesn't have enough eggs under her. Sometimes a Broody will keep adding to her clutch until she is satisfied she has a big enough group of eggs. This should not last for long though. A true Broody will not lay eggs anymore once she is sitting. When I put both my girls on their nests of eggs (11 in one, 10 in the other) neither one laid a single egg from the following day onwards.
Hope this helps answer your question? There is so much to learn isn't there?! Good luck with your girl,
- Krista