This is so sad, I too lost my lovely girl Ruby last year to the same illness she was 8, we fought for two years and spent a great deal of money on vets , tests etc,. I shed many tears ….I changed vets 8 times in that period as none seemed capable of understanding or any knowledge of the illness, although very common. I have her sister still who is 9 and suffers from Hypothyroidism, but fortunately although once again not diagnosed by the vets , I was fortunate to find facebook sites for both these illnesses and the knowledge from the people on the sites kept Ruby alive longer than she would have done, and again with Topaz, THEY diagnosed and recommend the correct treatment etc....My heart goes out to yu as I know EXACTLY how you feel, Topaz missed her sister for a while and became quiet and morose, now a year later despite all I said and thought we have a 4 month old girl called Amber, a gold sable lunatic, who is lightening the atmosphere, and above all lift Topaz, who has been brilliant with her.....However the paranoia of illness remains and everything she does I watch and watch....so the whole sorry episodes do not leave you and of course I miss my lovely loving Ruby, that will remain for ever!