Poor thing.. I think the responsible thing to do at this point is cull, as this affliction is very painful for the hen.
The swollen abdomen is a very classic sign of internal laying.
I am almost certain your hen is suffering from internal laying. Not a good prognosis at all unfortunately :(
So sorry...
https://www.backyardchickens.com/t/639749/timeline-of-internal-laying-update
http://www.avianweb.com/eggyolkperitonitis.html