First question, is she brooding in the house or out in the coop now? Second question, what day is she on?
Ok, now, going by my girls patterns and routines, the first 2 days they will not come off the nest, and I do not force them off. It is reinforcing that desire to sit. If on day 3 they do not get off I will remove them and not allow them back on until they have drank, pooped and at least got a quick snack. After that they will tend to get off once a day themselves to eat and drink. With Bunny brooding on the couch I would get her off, put her out the back door and when she did all she needed she was back flogging the front door wanting in. Towards the end of incubation they may stay off the eggs a bit longer and it will not harm them. None of my girls will come off the nest after day 18, and I will not remove them. If they were in a incubator it would be time to enter lockdown, and I think the hens know this as well. So that last day they come off, they gorge themselves, dust bath for a extended period getting ready for the hatch. I try to offer them water and a little bit of food throughout the whole process while they are on the nest. Some will drink and eat, others will not touch it until they come off the eggs for their break. As far as candling goes, you said they were dark eggs. I would not try then until around day 16ish. I candle at night with the lights off and a dark blanket over me. on those dark eggs by then, good ones will be black with only the air cell visible. A bad egg by then will light up like a Christmas tree.