Cat with Hyperthyroidism, now Ascites! help

My cat is 14 and has always been healthy up until about 4 months ago (November) when she became ill and was diagnosed with hyperthyroidism. She made a quick recovery when she was put on carbamizole and everything seemed fine and the vet was happy with her. Then I noticed about a month after she was on the meds that she was getting a little fatter on the belly, nothing major but noticeable to me and thought that it was just because she was eating more as the meds seemed to give her a much bigger appetite. Then in February I thought that something wasn't quite right and she had quite a belly on her and I took her to the vets thinking she had fluid in her abdomen.

They checked her over and took her for an examination and found that she did have fluid in her abdomen (ascites). They send her blood and fluid off for analysis. They suggested peritonitus, a problem with her lymphatic system or a tumour. In house tests they did on her blood showed she had good kidney and liver function and the xray had shown her heart was normal sized and that they couldn't see anything obvious in the scan. When her results came back they said she didn't have peritonitus and the fluid was chyle. She did have creatine kinase levels of 2500 when a normal level would be around 400.

They took her in to be drained and I was told to feed her a low fat diet of fish, chicken and they also gave me some special cat food. I have tried to keep her on this as much as possible. She was very thin when I took her home so it was pretty noticable the next day when they fluid had started to build up again. A week later she was back to the same size. She had another scan after the drain but they said they couldn't see anything unusual. Two weeks later I had her drained again.

She is eating and is bright eyed, still has a healthy looking coat, still cleans herself and comes for cuddles. However she is a bit cumbersome with all the extra fluid she is carrying about and is less active. She is looking very thin elsewhere though and has lost muscle mass. I have also noticed that she is drinking a fair bit and her poos are getting hard. I am also finding it hard to get her to take her meds as I keep finding she has spat them up when I'm not looking. She is also very grindy sounding when she eats.

I don't know what to do as the vets just say they don't know what it is but the chances are it’s not good and probably can't do anything for her. I wondered whether her thyroid meds have caused this problem but the vets say it isn't likely and won't entertain the idea. I also wondered if having her annual booster so close after being ill, she had it in December has done damage to her. In hindsight I wish I hadn't let her have it but they said it would be okay and that I should.
I know she just may be so ill there is nothing I can do but it would be easier to accept this if she wasn't so bright in herself. My friend suggested homeopathy as she has had successes using it for both her family and her dog. I know that it may be a longshot that it can heal her totally but wondered if there was anything I could give her to ease and possibly reduce her symtoms.

Any advice and guidance would be much appreciated.