I've called several vets, and they say, yes, it is quite possible. I attended a talk last night by a University of Utah Agent, a poultry specialist with advanced degrees in the area, and he agreed that it does happen. He doesn't know what my hen's outcome will be, and he said it will take a lot of energy for her to keep up the 2-egg per day pace. That is why I am trying to figure out the best diet for her. I have considered taking her to a vet to see whether she has peritonitis, but I'm afraid it might stress her out.
Did you read all the posts by members of this group in that link I posted just a few seconds ago? I would highly doubt that all 3 pages of posters would make up stories about hens laying multiple eggs in one day.
Maybe you are unfamiliar with the multiple-egg laying problem due to the fact the discussion of it is in the Chicken Behavior and Egg-Laying area of this group, not in Emergencies/Diseases/Injuries.
I loved the last line of one woman's post, but I can't verify that some hens who lay multiple eggs don't have her Betty's problem. I would love to be able to find out that multiple-egg laying doesn't spell pending infection and death for the hen. She wrote:
'Once, unfortunately for a sweet fun loving hen named Betty, 4 "eggs" were laid in one day by her. They had backed up due to the first one in line being malformed and once that came out, the others followed quickly on its heels (1 more malformed- a rubbery collapsed twisted shell with no content - and one soft shelled and one hard shelled). In the ensuing months, she continued to have problems and eventually infections that at first responded to antibiotics and later did not and then sadly, I lost her shortly after a surgery intended to relieve her of the problem (hysterectomy). But anyway, long story short, it is most certainly possible for a hen to lay more than one egg in a day. And hopefully, not necessarily because of a problem like Betty's.'