Thank you for the help Raze. I did indeed speak to Bertia about her missing sheep, I didn't realise I had handed her the corpse. Unfortunately, all my recent saves show the corpse as missing.
I am just going to take the opportunity to start the game from scratch. I'm disappointed to lose all the progress I have but I would rather not miss out on anything I may lose going forward.
I really appreciate your help, I'll make sure to email Larian with the issue. I can't be the only person who used the corpse as storage!