This is quite common with celebrities or page-3 personalities. They often smile falsely when in front of media (so as to come happy and photogenic!).
Is there any particular term for the 'smile for media'?
Note: I know the phrase 'reluctant smile' but then it refers to unwillingness and this smile is immediately caught by the opposite person. On the other hand 'media smile' is difficult to catch as it comes so natural (maybe, they are, after all, actors!).
I can say, No matter what has happened in her personal life, in her last photo, she had a media smile (not a reluctant smile, it does not fit or convey the message) on her face with no difficulty.
Best Answer
The term painted-on or just painted smile is sometimes used for this.