Thanks all. She was much better last night - didn't eat during the day, but gradually became more active and scoffed a bowl of minced chicken at 7PM. This morning she was begging for breakfast and had a sachet of wet food. She is using her box (I have put her in my bathroom so I can monitor her away from the others). Her coat looks better too - she is regaining her sleek look. And her ears are cooler. So I think we caught it in time. I will keep her isolated for another 24 hours to be sure and then it is just a question of completing the course of tablets.
She is out of the bathroom and delighted to be back with the others. All seems well and she is hungry and peeing in the right places. I am managing to get her tablets down her without any problem and she is being very affectionate. So I think we can safely say that she is well on the road to full recovery.