as far as JKR goes, she does adopt a it's-each-person's-own-business-if-they-like-this-stuff philosophy officially when it comes to fanfiction, but you can tell she's not particularly fond of it (flattered, maybe, but certainly doesn't want to read any of it).
when it comes to pairings, she pretty much sticks to canon and therefore odd pairings just seem really ridiculous to her (which is understandable, coming from a mindset where what she imagines is the absolute truth
). her reaction to Dumbledore/Luna was funny, which i believe she only became aware of because Evanna Lynch herself kind of ships them lol. less ridiculous pairing she tends to say "i could see that if.." or "i can see how people could see that, but.." like with Neville/Luna, Harry/Hermione and such.