I have let a hen that was under a year hatch chicks, and she did really good, and her baby went broody at around 7 months old and hatched chicks but sorta abandoned them a little early. I guess she tried and decided raising babies wasn't for her. I was really disappointed in her mother for not...
My rirs do the same thing! Then, as the heavy breed they are they accidently crush their eggs sometimes and give me more work. I think they are secretly evil.
I had same thing happen to two of my hens and they both hatched about 50 percent of their eggs. If you don't mind chicks I would say give her eggs. Also don't let me change your mind if you already made it up, I am a chick lover, I will do anything for them.
Put them in deeper type water, and if thet are only half submerged and the other half is above air they are dead. If they are almost but not quite all the way submerged they are most likely just hatching late.