I agree, not much you can do about it unless you can move the broody to a temporary nest spot so the others can't get in. The problem with another hen climbing in with a known broody is that she will lay her eggs in there too, which might result in a staggered hatch and that's tough to deal with. You could mark the broody's eggs and then remove any unmarked eggs daily, but with some broodies that's a little tough. My regular broody, Agatha, gets her name changed to Atilla the Hen when she's broody. Can't move her, can't check eggs, can't candle them, and smart not to even approach her unless you're wearing chain mail, gauntlets and a helmet. Yet she would also allow other hens to climb in the nest with her....go figger! Solution was a broody pen within the run and picking up the entire nest, eggs, Agatha and all, after dark. Otherwise as soon as her own eggs hatched she'd focus on taking care of the chicks, leaving the eggs laid later to rot. Not good. If she'll let you, you could even use a clothes basket or something as her temporary nest for brooding and put her eggs in there, surround it with some kind of pen, and let her do her mommy thing undisturbed. Good luck. Silly chickens!
