I think your Dumplin is not a Leghorn. They are a light weight laying machine. Large in the tall sense not in the round sense.
Make sure you grumpy hen isn't eggbound. Check to see if something is out of order in your chicken house. I am a newby at chickens myself but I have raised sheep for fifteen years and certain individuals at times take on leadership roles for the flock. I had the ewe, Mableline who would come and baa at me stridently if someone stuck their head in the fence, or they needed new water, or there was a lamb or goat kid (not her own) who was shouting for it's mother and mom wasn't answering. Some of her daughters and granddaughters do similar things like telling me when the water needs refilling. Make sure that you don't have a snake prowling around or a coon. She may be trying to communicate the only way she knows how that something is very wrong.
I have an old cat (he's 17) About five years ago he was following me around making me crazy with his meowing night and day. I would be working outside in the garden and he would come up in line of my vision and piss. It took me 3 days for it to sink into my brain what I was seeing. He was trying to piss and only getting drops out and then he would meow loudly. DUH! He had kidney stones! I real quickly dosed him with cranberry juice and got him some special feed for urinary health and in about a month he was right as rain.