Soft shell, membrane only then shell less eggs

Hi there,
Have got a problem with one of my. 10 month old light Sussex bantams.

On the first day we noticed something we got a fully formed Soft shelled egg on the grass.
On the second day we got what seemed to be just a membrane egg also on the grass. Today it's gone a step worse and it's completely shell less but in a nesting box.

In the mornings she had been fine, happy and normal. After laying the egg and for the rest of the day she seems like she's going to die, tail down barely moving little if any chase and closing her eyes. Each night I have thought to myself she might not make it through the night.

She is top if the pecking order, been laying for about 3 months. She's on a layer pellet and my other two are fine. This particular chicken has always had nice strong shells.

At first when I saw her I suspected she was egg bound, couldn't feel anything but gave her a long warm bath- but nothing.

Her vent is ver clear .

Any ideas ?
If she was egg bound could she continue to lay like she had ?
She's certainly suffering after laying and if she stayed like that overnight if be putting her out of her misery but each morning she seems fine...
The thing that keeps popping up in google is the infection due to yolk matter internally the is usually fatal. But since she is ok in the mornings I'm wondering if that makes that diagnoses less likely ?

Thoughts?