I only wondered as I've had a grossly overweight cat that I had to slim down, he weighed 2 stones when I got him and had actually lost weight previously. I've just looked on the iams web site and it says -

Medium cats, like the Burmese, Abyssinian and most unpedigreed cats should weigh 8 to 12 pounds.

Looking at her picture I wouldn't have said that she was overweight. I have a very square looking female who probably weighs about the same as your cat and she's not considered over weight. She's also a small cat as well, well a lot smaller than my other cats anyway.