Well,then she lied on twitter AND in NY times magazine,in which she has shown her remade ring

Her engagement ring is 7 carats, it wouldn't fit in this Cartier ring...
Dita's quote: "Prized possession: I took my engagement diamond and had it transformed at Christian Dior in Paris into a beautiful ring. It’s nice; it’s big. I feel like I suffered greatly for that diamond, and it needed to be reborn into something better."
Picture than went along with the article:
source:nytimes.com / TFS forum
The ring you're talking about is Cartier Secrets de Boudoir:
source:cartier.com
*** don't quote images. ***
See?