OK, question-----why would she come off the nest if she is being fed on the nest?? That will/can cause her to poop in the nest which can cause her nest to smell like poop/urine. I Hatch 100's of broodies, Never putting the feed and water close to her nest and I never see or smell poop/urine in their nest. If I was you. being it smells bad I would quickly change her nesting straw/etc(as long as you are not in the last 3 days), put her eggs back in, move the feed and water to the other side of her pen so she has to get off to eat/drink/poop/etc. Then """I""" would Leave her 100% alone---just checking her food and water. If you will pour her feed in a pyramid shape gently---then you will be able to see when she has gotten off to eat because the pyramid will be torn down.(being she is by herself).
Listen, she is yours, you can feed her, look under her anytime you want, etc, etc, etc Because she is yours. I have GREAT hatches never touching mine-----after the move to her private place. My Hens Do a Great Job alone! Good Luck
EDITED to add. I probably set more broodies than "most" on here, I have never lost a broody and have never seen one of mine that look unhealthy----I never take them off the nest--Never feed them in the nest--I just set them in their private place and leave them alone till I see her off the nest with her babies and they usually hatch 99.9 % of the fertile eggs "I" set under them.