Can I ask why? It wouldn't make a difference to her performances, so if she chooses to not use her scientific creds why should anyone feel the need to mention them? It doesn't validate her as a person anymore than if she was a talented actress who used to be a waitress.
I'm going to stuff words into ajays' mouth but if someone as "cool" as Natalie Portman can be so intelligent, that perhaps helps to counter a little of the anti-intelligence schtick that's common in some areas of life.
That said, many famous people are more qualified and intellectually agile than their public personas and media coverage give them credit for..
This is important if you beleive that 1) A society with more Scientist idols would get more scientists than one with more beauty queen idols 2) A society with more scientists would be a better place than if it had more beauty queens.
Because it would encourage a lot of people to become interested in science.
I could go on about how awful some movies have been but that's for another discussion.