Well, I would suggest anything by Takahashi Rumiko (Ranma 1/2, Inuyasha, Maison Ikkoku, etc.)
They're pretty fun, good stories, and likable characters.
Kimi Ni Todoke is nice too, more realistic characters than you see in most Shojo, and the storyline is kinda sweet...
But really, an interest in Twilight doesn't suggest a taste for cute or sweet storylines.
Show her Rosario+Vampire, she'll either squee over Tsukune in vampire form, or she'll get freaked out by the ecchi and never talk to you again.
Win/Win, in my opinion.
Cheveyo said:
Vampire Knight.
It is god damned terrible. She'll love it.
Basically, look for "Shojo" or "Shoujo" anime(they're the same word).
If you find a review for the anime and the review has anything that resembles "KYAAAAAA! KAWAI!!!!!! XD" in it, show it to her.
Or, if you don't have an
extreme hatred for those who like twilight (Ahem), listen to this person.
EDIT: Oh oh oh! Blue Gender! TONS of empty angst, forbidden romance, all the horrible stuff twilight girls like!
Plus it has a feel good ending!
*cough*