She could be broody, but since it's only been three hours, she might not be.
Sometimes they do sit there for a long time.
Are her feathers puffed? Could you attach a picture?
I have no experience whatsoever with an eggbound chicken, but if it proves to be that someone can help you.
She doesn't look overly broody to me.
She may just be showing signs of it.
I won't rule out her being eggbound because I have no experience with it, so wait for someone else to check that first.
By the way, I notice her back is bare.
Might want to keep an eye on your rooster. They can do some nasty damage.