Only one chicken with thin shells

[7 chicken army]

I am only having one hen that has very thin shells, when the other hens lay around it they break it and then it's a tasty snack. Why would only one hen have the shell problem? They eat feather fixer and I haven't been giving them scratch for about a week and it isn't helping. I will get oyster shell for them soon, but how can I make sure she eats it? Do they just know they need some? I do know which hen it is for what it's worth.

 

[aart]

Feather fixer should have enough calcium for layers....
......but putting out a separate feeder with oyster shell is fine, and yes, most will eat it if they need it.

How old is this bird?
Has she always laid thin shelled eggs?

If only one bird out of a flock that all have the same diet is having laying problems,
it's usually because that one bird has a defective reproductive system and/or a nutrient uptake issue.
...or she could be low bird in the flock and is stressed from being bullied.
Lots of potential causes/solutions....more info about bird and flock would help to maybe pinpoint the issue.

 

[7 chicken army]

She is in her second summer. I don't think she's always laid thin shelled eggs but I'm not sure I would know if she was, if the others have been eating the evidence. I think she's one of the higher members in the flock, actually. Something else weird, one of my other hens has been laying long eggs, weirdly shaped, but only since about the beginning of July or so. I can't see anything going on that's only been going on since the start of the summer that might be causing these two things, so not sure if they're related but I thought I'd throw that in. The other thing is, five of my hens are orpingtons and the one with the long egg and the one with the thin shells are both orpingtons, so while I know the one laying the long eggs is not the same hen as the one laying the thin shelled ones, I can't really tell the thin shelled ones from the other regular orpington eggs, so I'm not positive that she never lays regular eggs. I can say it seems like my egg production is less than it ought to be. But I don't have proof.