Rusty's waterworks

My rescue girl, Rusty, has an ongoing problem with her waterworks.
As I am aware, chickens don't pee - but someone forgot to tell Rusty! She passes a lot of water & consequently drinks a lot as I figure the kidneys may not be functioning properly. She had a course of baytril and the problem seemed to clear up, faeces firming up & urates starting to form, although still a bit loose. That was a couple of weeks ago, but now the anti-b's are out of her system she's back to peeing water again, sometimes with little clumps of faecal matter in, sometimes unformed, and this morning just liquid! She drank about 100ml of water with Avipro plus in it and less than 5 min later she passed most of it back out again. The strange thing - as if that wasn't strange enough - is that the water was still cold, hadn't even got up to chicken temperature, and was mildly cloudy.
I've rung the vet and told her, she reckons that somehow the water has even managed to by-pass her kidneys, having passed through that quickly. She's put me up something else to try her on for the time being (don't know what yet), but I wondered if anyone else has come across this. Looking through the Chicken Health Handbook shed no light on it for me, and I checked out all the stuff on dehydration, diarrhoea, increased water intake, etc. Mind you, it's not diarrhoea, it's clear/milky liquid. Am v puzzled...
Oh, she's one of the 3 that aren't laying & hasn't since she moved in in March (not fussed about that) and apart from that seems very healthy. Any ideas?

Yes, I refer to that whenever I'm baffled by what's passed - it was how I found the site in the first place last year, by typing in "sulpher yellow chicken droppings" on Google, something I never thought I'd have a need to do... Rusty's aren't there - but will be when I finally get my head round posting pics (pc incomp!)