Coincidentally enough, she just asked me to let her watch Halloween 2 again, but I helped her change her mind. Now she's in the den enjoying Hooper's TCM2 for the first time. She laughed her head off at the "Frat Boy" intro. I had suggested either Shaun of the Dead, or Return of the Living Dead. She picked both of those along with TCM2 as her preferred choices from what I had offered, then I mixed them up behind my back and had her pick a number.
I'm rather certain she knows far more about film than the average 7 year old. I even showed her the knife gag with the tube attached to an ear wash bulb filled with fake blood last Halloween, and she absolutely loved it. I haven't shown her my Savini FX books yet, though, as she still tends to mangle just about everything she touches.
She hasn't had a single nightmare as a result of anything I've let her watch thus far, although she did start to tear up just a bit the first time she watched H2, but that was only because the volume was too loud and she was tired and cranky because it was so late. The very minute she returned home from school the next day, she begged me to let her watch it again. She made it all the way through sans tear or fear on her second attempt. I told her I was very proud of her for that. She still has to conquer her fear of Romero's NoTLD, though... but she has plenty of time.
H2 and the TCM remake are definitely the harshest films I've let her see, and yet oddly enough, she had no problem with TCM whatsoever. The zombie films are the safest for her IMO, but she's not getting to see Fulci's ZOMBIE anytime soon. I have deemed the original Evil Dead off limits for now as well.
It bears mentioning that insofar as PG-13 films go, her favorite is Big Trouble in Little China. She still watches the Twilight series and Miley Cirus vehicles and whatnot, but those films and their ilk (As well as The Disney Channel) can't possibly compete with her interest and enthusiasm for horror, and that just tickles me to death.