Actually, some hens Do crow. We had a mutt hen that laid eggs and crowed every morning. She was an only, so that may have had something to do with it. We got her as an adult from our local humane society (who foolishly told my youngest daughter "If you can catch it, you can keep it" - enough said).
I called the humane society where we got her (had no info for us - maybe she is really a he? - really? roosters lay eggs???)
Called Several Vets in the area. The farm vet told us "yes, hens can crow. Try giving her layer pellets as that may help with "rebalancing her hormones. This is only the third crowing hen I have heard of in my entire life." (they didn't)
Called animal control before the neighbors could to explain the situation (they were surprised that our "rooster" laid eggs)
Called the neighbors to explain that yes, she is a hen that lays eggs. we don't know why she crows or how to stop it, called animal control, several vets and the humane society and got very little help, but we will try. They didn't believe us either.
She finally stopped crowing when she was taken out overnight by feral cats. She would insist on roosting high up in a large oak tree and we couldn't get her into a pen no matter what we tried. She was a cagey bird for the most part.
Edited to add: Her crow sounded like the first crow a cockerel makes - a rather gurgly cock a doodle doo. (really more like err erooo)