Yes, she was checked for thyroid etc and pronounced ok. The only thing that showed on the blood test was the high salt level.
We are giving her the vet's low salt diet where possible, but of course being from the vet it's expensive, and they only have a couple of varieties. Therefore we are still giving her some normal foods as well. She's so obsessed with water she even jumps up onto the sink and attempts to drink from the tap !!
Still, at least that shows she's still fit and supple. Hopefully, we'll have her for some time as we also have her younger sister, and I wonder what the effect on the younger one would be if Penny were to die.