Casportpony can give us more on this----I did the necropsy of a sort.
In this picture---slightly below middle is a stack of egg shells that I broke apart some before I took this pic. Looks like a egg tried to pass and stopped, then the next egg broke/crushed the shell at the top and stacked...
You know me good enough to know I am no doctor---the way this OP described the symptons---sound the same as this chicken. Might not be---But this chicken could have been soaked until the feathers came off----it would have never dumped this.
She is probably ok with them----if this is what I described--the egg bound is different than your normal egg bound----she is probably producing shell-less eggs and they are just building up inside her---which is what is making her heavier and hard. Let me find a pic-----not a pretty site though.
Probably what I call extremely egg bound, internal laying but none coming out----she just gets heavier and heavier until she can barely walk but then walks like a penguin when she does try to walk??? Could be water belly, but being you said Hard----I am thinking not. If its what I just...