There are a couple of things you can do. When they start hatching, you can take the babies from her as they hatch so she will continue to sit and hatch as many eggs are viable at hatching time (it will be a staggered hatch because they are not all at the same stages of incubation, having been laid in the nest over a period of time). Or, you can let her keep the first-hatched chicks and be prepared to incubate the later ones, as she will most likely take her chicks off the nest after a day or two of hatching. Or, you could scrap the whole bunch of eggs, and start her over with 8-10 eggs (if she's a LF bird), mark them and daily remove any extras that are laid in the nest. The problem with 30 eggs is, she most likely will not be able to hatch them all as she can't effectively cover them all and keep them all warm. Some will get pushed to the edges and the developing chicks will die. Then, as she's rearranging and turning her eggs, the dead ones will end up under her, and more will get pushed to the edges and die, etc. If you want to let her try to hatch them, though, go ahead but mark them so you can remove extras when other hens lay in the nest.