Cat sickness

[d1g1t4l5w1f3]

My mother rescued a siamese cat, holly last year, she is 7 years old and apart from having some teeth removed, there was no reported problems from the person we got her from, we took some food from her former home and bought the same when that ran out (hills chicken) mum had her spayed the next month (she had been used for breeding) but the problem is since my mum has had her, holly has been sick nearly every day, mainly in the morning, sometimes bringing up food sometimes just liquid, On the advice from the vet mum changed her food, but no improvement, over the last year, we have tried 3 different types of hills(one of which was a special prescription diet from the vet), imams wet food, and burns food, none help her, she has had the last of her teeth out, as there were infected, had blood tests,a chest x-ray, a nose swab, and a camera/x-ray up her nose, all come back normal. A visiting vet told my mum holly had slight asthma and gave her a injection, which made her poorly, and on her return the normal vet said she could not hear wheezing and there was no asthma!, but we are now at a loss of what to do, the vet is trying yet another hills diet-venison and pea, but she is even sick on water sometimes, so we don't hold out much hope, is there any one who has had the same? or has any ideas? She is a wonderful cat, and improved my mums life no end, and is a healthy weight, bright and talkative, her coat has a slight sheen and she has dry skin/dandruff so nothing really unusual, just this up setting sickness.
Any help greatly appreciated

[fairkatrina]

Get your vet to test her blood for kidney problems. It's unlikely as it has gone on for so long without having a detrimental effect on her overall health, but it's worth a try.