Super thin eggshells

My Wyandotte keeps laying eggs with extremely thin shells, often they’ll be broken in the nesting boxes even. They all have access to oyster shells, and I do refill it often so I know some are eating it. None of the others are having these issues, so I’m concerned! I don’t want her to have any internal health issues, does anyone have any ideas? She is 2 years old and laid normal eggs all last year.