Soft shelled eggs???

Ok, I've done some research. And am needing some help.
Our hen "Tuesday" has not been laying much and when she does they are soft shelled, well basically no shell. She is about 2 or so years old. She does have some other issues too. She cannot see well. We haven't determined exactly why, but for example if you try to hand feed her she will end up getting you hand too, where every other chicken we have can peck treats out of my hand no problem. I've also noticed it when she's eating something off the ground that she will sometimes miss or have depth percecption issues thinking it's higher than it is.
She did have lice about a month ago, but we seem to have that cleared up and still the eggs are this way.
The chickens have layer feed, plus free choice oyster shell/chicken shell.
None of our other hens are having any problems, and actually I've noticed a few whose shells are becoming thick and take an extra whack to crack!
I'm out of ideas as to what to do to help her...

I have a Black Australorp hen that is now 2 years old. She began laying very thin shelled and shelless eggs at a very young age, although not frequently. When she was about 1 1/2 years old, the frequency became regular. Eggs with just the membrane and even just a yolk. I would find these eggs in the run, or in the morning beneath the roost bar and sometimes she managed to get them in the nest box. She was and is on a good layer feed and eats well, with plenty of free choice oyster shell always available.

Well, I thought maybe she might grow out of this, but it just continued to the point of her constantly going into the nest box trying to force eggs thru her system. Day after day, week after week this was the scenario. So I talked to my avian/poultry vet about it.

He says that this can stem from a few things. It may be as simple as an imbalance of the minerals and amino acids in the feed....the calcium, magnesium, phosphorus and amino acids must be in the proper proportion for the hen to get the shell on correctly. (Consuming more oyster shell was not the answer in this case). This issue could be caused by genetics, as it was passed down to her from the parent birds. Or this issue could stem from a defect in the shell gland which can also be genetic. If the hen is carrying a genetic issue, there is only so much you can do.

So, he sent me some solution of liquid calcium, phosphorus, magnesium and amino acids to put into the water. She has improved to the point of at least she can now put a shell on the yolk. I thought over time, (it has been several months) that this stuff would have built up enough in her system to have her laying harder shelled eggs, but they are still coming out funky and thin. She still goes into the nest box and strains, only to NOT have laid an egg. But when she does lay one, it has a shell on it. I am not sure how this will effect her as the year or years go on. One of these eggs may be the death of her. But I have not found any shell less eggs or yolks anywhere around. (thankfully none of the other chickens have found then either...LOL I hope they all stay dumb to this egg thing. LOL)

My flock as well, all lay very hard shelled eggs. I don't know if your hen is suffering from the same issue as mine, if I am able to figure out what the deal is here, I will definitely share the cure with you.

Please let me know if you learn anything. I am wondering if it's genetic or something. However she's been laying fine for a year with a soft egg once in awhile and now it seems that is all she lays.

While a lack of minerals can cause hens to lay soft shelled eggs, soft shell eggs are usually the result of disease, old age, or obesity. It can even be the first symptom in the onset of a very serious poultry disease, New Castle.

The straining may mean that your hen is having problems forcing an egg past the fat in her abdomen, or it could be that she is straining against the fat to hold her eggs in until a shell can be formed. At any rate too much abdominal fat can cause eggs to be laid prematurely.

Old age may or may not be the reason in the beginning post but in a young hen like twocrowsranch's bird I would think that maybe she has one of the chicken herpes viruses. If she is infected by a virus there is no treatment that will kill the virus without also killing the hen.