Sad to say she relapsed again this pm 
. Went all quiet and sad, then laid a no shell egg. Thats two eggs in less than 6 hours. I think she has a problem
I shouldn't worry about 2 eggs in 6 hours - doesn't happen often, and sometimes means the second egg is thin shelled or absent as the shell gland might not have enough calcium soon after laying the first.
EDIT: I should mention that a double yolker is basically 2 eggs in one so something similar
I had a layer that was productive for about 19-20 months then went through a shell-less or thin-shelled egg laying session (some eggs were huge too!) over a 3 month period before thankfully she stopped altogether. Within a few weeks she went into a full blown moult well before the others and then a few months later in late winter, started to lay perfect eggs again.
She used to be the top hen more by accident than design by beak butting others out of the way of her food LOL but the deputy hen was mean and vindictive (feather eater) and eventually wore her down and out of her prime position. I often wonder if it was the stress as she was an easy going hen - stress can upset the natural rhythm of their cycles as well as immune system. Heat stress would do something similar. Also, up until then she had been a good layer so basically she needed a rest to recover as it takes a lot out of them.
Do you put apple cider vinegar in the water? Might be worth withdrawing that especially during hot weather as acidic conditions reduce the amount of calcium that can be absorbed. Maybe a little dose of cod liver oil (don't over do it and only now and again) in the feed such as a mash made from the layers pellets to help with calcium absorbance - if calcium levels are low, it can be taken from bones so it's not just about increasing calcium in the food which too much can be bad for their kidneys but also vitamins too.
