You've had Tess for 8 months - has she been "calling" at all in that time? i.e. has she been meowing a lot (for about a week or 2), craving affection and off her food? If so, she's been in season and is obviously not spayed. If she hasn't "called" then you can safely assume she has been spayed. You probably know this anyway. You say she looks "different" - how? If you're anything like me, it'll be difficult to put your finger on, but you know when your cat isn't "right". I think you're right to take her to the vet and I wish you the best of luck. Please keep us posted as to the diagnosis, won't you? K xx