What's wrong with Lulu?

Please could somebody advise me?
Lulu is a 21/2 year old White Star and some of you might remember she damaged her leg some time ago. She has completely recovered from that and was back to her old self for a couple of weeks.
Then her egg laying stopped but I was finding broken soft eggs in the coop. I thought it was the young Speckledy starting to lay and didn't think anything of it.
Then one afternoon I noticed Lulu's bum was covered in creamy white stuff and what looked like a small pale pink lumpy bit sticking out.
I got her out of the coop after dark (she's pretty flighty!!) for a look and feel but couldn't find anything (the "lump" had gone back in so could've been the vent) so gave her bum a good wash.
Since then I don't think we've had an egg (13/14 days) although it's difficult because we've got 2 White Stars. Lulu's eggs are larger...in fact one of her last eggs was 90g.
Now she has good days and bad days....tail up or tail down, running about or being tired, eating like a horse or just pecking a bit, out with the others being normal or being a loner and going in and out of the nest box.
I poked my head in the nest box to see what she was up to and she got up and left a puddle soaked in the straw that consisted of the creamy thickish stuff, a load of clear watery stuff and I found a small jellyish splidge of greenish slime. It didn't smell at all so I assume it's egg based rather than poo. Her poo on the grass is in the normal range and they've been wormed etc.
I can't put my finger on what's wrong because although I know she's not herself one day, the next she's a bit better.
And however she feels she still comes running when I call at treat time, even if she doesn't eat much!!!

Sounds like she is laying shell less/ soft shelled eggs.  The protrubance you saw is a prolapse caused by the straining to lay the egg.  I assume she has access to oystershell but if not your could try adding limestone flour to her feed for a couple of weeks to ensure she has plenty of calcium.  Also a tea spoon of cod liver oil in the pellets will give her some vit D3 which is necessary for calcium absorption.  Should she prolapse again you should use a greased finger (lubricated with Preparation H haemeroid gel) to replace it.

Keep her under observation to ensure she's not egg binding which can lead to peritonitis a serious internal infection caused by the egg becoming infected within her body. Antibiotics from the vet quickly administered would be needed if she gets egg yolk peritonitis (EYP).

Her egg laying days may be over or she may recover and her laying vigour be restored after a moult, you'll just have to wait and see.

Best of luck
HF