I doubt she reads the fanfics. With over 200,000 HP stories on FF alone, someone was bound to hit real plot points. Many people have predicted Snapes unending love of Lily Evans Potter, for example.
Though, there was a few times where I thought she might be nodding to the fanfic folks. The line about Snape after he jumped out the window: "With a tingle of horror, Harry saw in the distance a huge, batlike shape flying through the darkness towards the perimeter wall." I'm pretty sure she described Snape as batlike in the first book, but the fanfic authors have run away with it.
2 outstanding questions have come to mind:
1) Does the Sorting Hat summon the Sword of Gryffindor from wherever it is? Or did Griphook bring the thing back to Hogwarts (which seems HIGHLY unlikely after the description we were given of Goblins motivations.)
2) We know from book two that Colin Creevey's father is a milkman, and it says he's Muggleborn, as he was a victim of the Heir of Slytherin. If he really is Muggleborn, how did he end up at Hogwarts for this book? Or did I miss something. I thought they stopped anyone without direct proof of wizard relation from going to Hogwarts or anyplace else, for that matter. Does this mean Creevey is a Half-Blood?