Looks like albumen and extra membrane.
Counter peristalsis.
Fully shelled egg backed up in the system and got more albumen and membrane.
Are all her eggs like this?
How long has she been laying?
Not sure what can be done about it, other than hope it works itself out.
I think you are right. I looked again at the photo more closely and can see membrane now.
It's an egg within an egg (at least a shell-less one with no apparent yolk)
I would be worried if it was every egg and going on for several days, rather than a one off aberration. Not sure which it is.