Ah the joys of the not so pleasant broody poop … yep, that stuff can make your hair curl
You will no doubt have read on numerous threads that broodys will vacate the nest at least once a day, some moreso, to have a drink, something to eat, a bit of a walk around, dust bath and deposit one large, extremely odourous broody poop etc. These breaks can be just a few minutes and sometimes 30 to 40 minutes.
You will no doubt also have read that even though you may not see your broody do this; she probably does.
However, there are exceptions to this rule and I have one!
Cilla does not leave the nest of her own accord. On her first hatch I gave her three days to move on her own and she did not .. she gets so deep into the broody zone and would sit there until she starved.
So, my trick with her from that hatch and hatches following is to move her off the nest, once in the morning and once in the afternoon. When I put her down on the ground she will sit there for a while in that broody heap you describe but after a minute or so, snaps out of her trance, has a bit of shake and gets her legs moving.
I place her away from the coop with water and food containers available between her and coop. This way, her legs get a stretch, she usually stops off for something to eat and drink on the way back and deposits that poop.
Your broodys desire to get back to her eggs should encourage her to snap out of the zone and have a wander.