Bossy bird lays thin eggs

[Mississippiwoman]

Hi there. I just started on this chicken thing, one of my australorp hens, who considers herself the boss of the other hen and pullets, lays very thin-shelled and faintly-colored eggs, if she lays at all.

I got her and another hen from the same place in May and the other one lays great-looking brown eggs (though she hides them and doesn't like me taking them).

Could she be laying thin eggs because she's a few years old? I give them oyster shell, powered calcium and have tried putting cider vinegar in the water. Anybody out there have any ideas of what I should do?

Thanks for your help!