Thanks for that New Shoot and I had looked at that before for some clues.
I have done some more research and what she had passed appears to be the whole of her small intestine (small as about a foot and half long)
I change their litter tray (for sake of a better word) directly below their perches at least once a week and have a poke around and nothing over the preceding time in the quality of droppings indicated any concern. Eating, drinking and boisterousness wise she was no different until it happened.
The sequence of events from what I can surmise where, went to lay an egg (but didn't) and exited the egg box leaving a small drop of blood, started to walk down the ramp and passed her intestine on the ramp and then just sat huddled up in a corner.
The other two seem fine and I had all three together from 'The Gobbett' Kidderminster and they have been inoculated.
I can't seem to find anything on the internet as to why a chickens small intestine can become detached from the gizzard and it does not appear to have been caused by an egg getting stuck as she did not lay one that day and there was no preformed hard shelled egg inside her when I looked.