sorry to hear about your friend's cat. I presume the vet has ruled out a heart condition causing this chylothorax? I expect so, but thought I'd ask because this is exactly what my Sam had - and he has hypertrophic cardiomyopathy (enlarged heart) - this was diagnosed with x-rays and scans. I guess if they've said its idiopathic they probably have ruled out heart problems. Sam had to have fluid drained off and it was confirmed as cylous fluid.
Sam is on the same meds - Fortekor for his heart, diuretics and Rutin. He was jut on fortekor and diuretics to start with, then I researched about the Rutin and my vet said I could try it. I also put him on 500mg of taurine once per day - and I started to see more improvement about a month after I started the Rutin and taurine. His appetite picked up and he was much less lethargic.
He did have an episode a few months after diagnosis (which was back in Aug last year) where I thought the fluid was building up again, but my vet said to try increasing the diuretics for a few days, and that seemed to work and we didnt need fluid drained. It was after that I started the rutin and taurine.
I found putting Sam's tablets in cheese (moulded round them) and giving them to him before food works best. The Rutin tablet I crush with a pestle and mortar and put it in his food - he doesnt seem to notice it and the same with the taurine - but of course thats only poss if a cat is eating. Initially, I had to give Sam his tablets straight in his mouth because he wasnt eating properly. The one food that I found really kickstarted his appetite was Applaws tins fish variety - so that might be worth a try. I also found, while his appetite was still a bit dodgy, if I sat with him and really encouraged him to eat,- sounds daft I know, but I sat down on the floor with him and it really kept him eating rather than walking away from his food.
Has your friend's cat been on the treatment for the two months or is it still early days?