First of all, she’s 7 and the film is rated PG-13. Second of all, she absolutely ADORES Anakin–especially the younger Anakin in EPISODE I.
I don’t need to tell you that things aren’t all hunky-dory with Anakin. She knows it, too. She knows what he becomes, and she knows that Vader is evil and needed to be stopped. She knows that the little boy who won that race and hugs his mother becomes the most vile villain in the galaxy, and she knows he’s going to hunt down and destroy the Jedi Knights. But, despite knowing all this, I think she’s going to struggle with his downfall.
That being said, she can barely wait to see the movie and we’re going to take her. Her brother (age 10) is also all geeked up, and I got him LABYRINTH OF EVIL, the pre-EPISODE III novel, for his birthday.
If you, too, are concerned about the PG-13 rating, TheForce.net has a summary of the worst parts. They’re bad but not awful. Of course, this is SPOILER TERRITORY, so only follow that link if you want important details given away. Really.