Just a quick update. My cat has been diagnosed with a Hyperthyroid.

4 months ago, I was concerned as my cat was grinding her teeth when eating wet food (which started this thread). I took her to the vet, who had told me she could be stressed.
I was slightly concerned as she was beginning to loose weight. She started being fussy with her food, until I changed her wet food to another type of wet food, which she was eating lots of, but she was still loosing weight. I monitored her weight loss over 3 months with monthly visits to the vet, and she got down to 4.2kg! I had blood tests taken, and she was diagnosed with a Hyperthyroid.
She is now on 2 tablets a day, and she has gained 500g in 1 month. She has recently had further blood tests and this shows that her kidneys and other organs are all ok. My next step is to decide whether to continue to give her tablets for the rest of her life, or to have an operation to remove one of her thyroid glands.
In the meantime, I have decided to continue giving her the tablets and let her have a rest for a few months until I decide what I would like to do.
My cat no longer grinds her teeth and is living a happy healthy life.

The reason why I am telling you all my story, is to advise that if you notice any difference in your cat, please take him/her to the vet. Even if it's the slightest thing. At the beginning, I was told that the vet couldn't see anything wrong with my cat, but as the owner, I just knew something wasn't right. Over the next 3 months my cat drastically lost weight, and I believe that due to my persistance and us diagnosing the problem immediately, this saved her life.