Sorry about your hen. I agree with others to get a necropsy if you can, sometimes it can be reassuring to find out that it was some cause you couldn't prevent ie internal laying etc. You did your best in caring for her regardless, sometimes we are just not on the side of luck and end up losing them.
One question I have - what is 'strong electrolytes'? I thought electrolytes solution is a proportion of salts in water for hydration, if you make them any stronger, that's just salt water, isn't it? Or is it a specific product?