A problem for movie stars is that when they've already created successful careers (with an Academy Award in this case) their appearance has been established in the public mind. If they have plastic surgery to look different, even if it is subjectively an improvement, it's not THEM, not the person whom the public and their fans expect. Not the appearance associated with their distinguishing roles.
It's a high-risk move, and often not successful. If you're gonna have cosmetic surgery do it before you enter the public eye, in order to build your career, not after you've already got one. Once you establish a persona, stick with it.