Lift her off the nest twice a day for 10-15 minutes. She will do an enormous and very smelly poo, and should have a drink and some food, and stretch her legs a bit. She's obviously sitting very well, and will be going into a sort of trance on the nest. The eggs won't be harmed by a few minutes without her on them, in fact some modern incubators build in this cooling time to their programs as it helps hatch rates. Sitting does take it out if them and she will lose weight, but will put it back on when the chicks hatch if you let her eat the high-protein chick crumb that they need.
Get your chick crumb ready before he hatch date, now she's sitting tight, and make sure it's well in date as out of date feed may harm the chicks.