Hi Glenys and welcome to the Forum.
I've moved your topic to the Chickens Health section, as I think you may get more replies there.
This swollen abdomen problem is quite common in older hens, particularly in hybrid layers that have always laid regularly. As they reach the end of their laying ability, they are prone to complications such as egg peritonitis, which can cause the symptoms you describe. See the article in the main Poultrykeeper website, here http://poultrykeeper.com/reproductive-system-problems/egg-peritonitis
I'm sorry to say that for such hens the future isn't good, and if indeed the hen has this complaint it will cause considerable suffering and there is no cure possible. Of course this may not be the case with your girl, people on here who haven't seen the hen can only suggest possibilities , and only a vet could give you a definite diagnosis. If you do take her to the vet and he or she says she has a limited time to live, of course you have the option of letting him put her to sleep painlessly if you're not up to the job yourself.