They say broodies usually get up once a day. If she is really broody and someone does manage to get her off the nest, she will go back within a few minutes. I feel they need to be able to stand up and move around, as well as eat and drink when they feel the need. Being broody is hard on them; they lose weight and muscle mass, among other things. I actually take mine off the nest whenever I go to the coop, though they can come and go on their own.
I take mine off the nest once a day if she's where she can't get out on her own. Even so, I watch and see if she gets up or not sometime during the day. Some don't and will stay for days. Best just to pick them up and take them out of the coop once a day to be sure, I think. Course if a person had dozens of them, that would be pretty impractical.
hmm. I was gone while my silkie was on her eggs, so I have no idea what she did. I made sure she had food and water that the others couldn't get to, and her eggs hatched a few days after I got home. I wouldn't stress about what your broody is doing.