I don't think that a crowing hen is too uncommon, it does happen. I've been wondering if it's something to do when they're alone? I've had bantam hens crow. Here's a video of one of them crowing:Well I didn't expect this.
One of my newly acquired Cochin mix bantam hens, Mipha, was just having a crowing match with my younglings.
She's also spurred.
I have no problem with it whatsoever. She can sing right along with the choir. It's very interesting though.