Well... If she like sports, Slam Dunk or Dear Boys
(or the Dear Boys: Second Act, although I recommend getting the first part first...).
But if she's a soft-type, The Sailor Moon series is nice.
Slayers are good too. Never failed to make me laugh.
Detective Conan, the first Manga I read... The best thing about it, there's no ending yet! (The current volume is about 40 or above...)
I would also recommend XXX Holic and Tsubasa Reservoir Chronicle from Clamp, but I don't think she should read these, expecially XXX Holic. It could be misleading sometime.
Good luck on your search. (Heart)