I'd have to say that I don't think she's had a nose-job, or if she has then it's
very subtle. Personally, I think it's more to do with lighting and make-up.
Now, in the photos post #1 she looks like she may have had a nose job, but given the more recent photos where she's just "out and about" I'd definately say she hasn't.
Check out these pictures from January/February 2006; she's got the same shape nose as she had back in 2002.
I think it would be a mistake to change her nose, as with Sarah-Michelle Gellar). It's part of their charm.