It's probably too small for her now (in terms of carats). The smallest stone I've seen her wear recently is the 5 or 6ct radiant canary diamond. I am, however, loving her new ring. Amazing!!!
I'm pretty sure this ring she's wearing (in the pic debuting her new cut) is borrowed for fashion week / for the runway show. I read that it's chopard i believe, though i'm not positive. but we should start a thread for borrowed jewels that celebs wear on the red carpet, etc!
http://offtherack.peoplestylewatch.com/2008/09/09/victoria-beckhams-new-short-do-think-gamine/