my experience (with my banty) is when she went broody and was sitting on eggs she waited till about 4 eggs hatched and left the rest, I guess she didn't want to be a mother to more than 4, she didn't give the other eggs time to finish hatching. now what ive heard from others is they will still take chicks and sit on eggs at the same time until everything has hatched. I have not been lucky enough to have this happen to my chickens but some are lucky enough, so I would have to say that it just depends on the temperament of your bird, it will be a gamble so the only real way to know is to let her tell you. (not through words just by observing her lol)