It is possible she is just enjoying helping set the eggs......I've had hens do this.So I have two broodies right now and I estimate the hatch date to be tomorrow (although I'm not sure exactly what day they started sitting). One is a cochin, the other is a turken. This morning the chickens were out free-ranging and I heard an egg-song. I'm not getting many eggs these days (moult, reduced daylight etc) so I popped out to see if I could figure out who had laid, since I'm curious to know who my best layers are.
I couldn't find an egg! I looked in the nesting boxes and the other places that some of my goofball hens prefer to lay, and also all around the yard. The Turken was out ranging with them and was still singing the song long after everyone stopped (she continued intermittently for at least 20 minutes). This makes me think she was the one who started it. I took the egg (only one left, a few got kicked in a kerfuffle with the other broody) and put it under the Cochin since the shell was starting to feel cold and I was afraid she had abandoned the nest.
Has anyone else had a broody sing an egg-song, or be the instigator? Makes me think she stopped being broody... she's been the flightier of the two broodies, spends a lot more time off of the nest, etc. We don't have them segregated from the flock or from others since we weren't really prepared for this and we're just rolling with it to see how it goes (our first time).
I have one now that sets on the eggs when broody goes to eat and do her thing........will set there for a bit when the broody returns then goes on her way......
They are all is individual............it's fun to watch them.................good luck with your hatch........