For me, the biggest change is her chin. It completely reshapes her face. The cheekbones take away the moon-face thing, too.
Her mouth does look a lot better - it doesn't protrude as much compared to the rest of her face. That may be because her chin and cheeks stick out further, though.
She also had some work done on her eyes - they are less hooded and fleshy than they were before.
I think that she looks very good. Not fake at all, and she still looks like Chelsea. Just better.
And who can blame her for having some surgery. With her parents, it almost would be a necessity. :)