I'm playing with the idea of a MG character who channels characters from famous literature/movies/TV shows when she's under pressure and not sure how to handle a situation. For instance, she might ask herself, 'What would Katniss do?' or Hermione, or Coraline, or even Catwoman. Would this be a problem, copyright-wise? Thanks!
(Ritual IANAL disclaimer)
I think you can say stuff like "What would James Bond do?" or "who do you think you are, Buffy the Vampire Slayer?". At least, that sort of stuff is often said in books and films without any apparent legal difficulty. Where you'd get into trouble would be actually having Bond or Buffy appear in your story.
There are shades of that; you can have tuxedo-wearing MI6 superspy John Bell show up, I think, because the elements in question - tuxedo, MI6, superspy - are pretty generic. As soon as Bell starts ordering vodka martinis, shaken not stirred, and introducing himself as "Bell, John Bell" then you start to sail closer to the wind. (Check
thisout. Looks like they got away with it, though.)
(On Holmes, there are further wrinkles because the earlier stories are out of copyright, but later ones are still in. So though public domain uses of Holmes are all over the place, and it basically appears you can do a lot with the character without having to get anyone's permission, there are legal complications; there's a case in the US at the moment, I believe, which has been brought specifically to clear up the issue of whether anyone has a real claim on the character.)