Pretty weird that Heather. It is essentially a 'lash', which is shed oviduct lining. But it appears to have an egg yolk and flesh in it. We have had something similar when one hen shed her entire oviduct system, but ours was a bloody mass on the outside. The flesh areas may be tumours or cysts? She has shed it for a reason, so clearly it wasn't right.
Interesting to see if she lays again? They usually do a month or so after laying a standard lash.