Check out this letter a fan of a book series "geared toward younger readers originally" wrote to Ask Amy. While Ask Amy automatically assumes that the letter-writer a die-hard Twilight fan, however, 'Obsessed' could be... well, obsessed with any number of series:
Goosebumps. R.L. Stine (pictured right) is a sexy beast. (I know, I know, he isn't a character, but that picture seriously cracks me up.)
Harry Potter. If anyone is actually obsessed with Harry Potter, she obviously hasn't read Order of the Phoenix, when he becomes the biggest whiny bitch in the entire history of literature. That's right, the entire history of literature!
The Chronicles of Narnia. I guess it depends on which character she loves and whether or not she 'gets' the metaphor, but let me just put this out there: bestiality is never okay. (I will, however, admit to having a slight crush on Mr. Tumnus in the most recent film adaptation, but can you blame me? I love me some James McAvoy, cloven hoofs or not.)