She was laying fine, so I would assume her apparatus is OK. You said she's underweight; that points to infection or disease possibly. Besides deficiencies of x or y, spells of laying soft- or shellless eggs can be triggered by Mycoplasmosis synoviae. Does she have any sign of that? snuffles? occasional sneeze? just under the weather? If she does, it's not fatal or damning; she may just go through cycles of this.

They can have mild MS which impacts the laying but has few other telltale signs.