Kate was photographed wearing this cuff bracelet a few times prior to 2008.
It’s on her right wrist.
Here is a close up:
It looks to be a thick silver metal cuff bracelet. There might be small detail at its edges, although I am not too certain. The bracelet does not close fully around the wrist because it’s a solid metal bracelet and not stretchy. It’s the same bracelet she’s wearing in the photo below (also on her right wrist).