I think I can help -- I've got a 14 year old and a 17 year old, both girls, and I read a lot of "young adult" fiction.
See if she's read anything by Tamora Pierce. All of those are pretty good. She might also like Mercedes Lackey, both the Valdemar books (romantic fantasy) and her fairytale retellings. If she likes Robin McKinley, she's also likely to like Patricia McKillip. I would also suggest Terry Brooks' "Tiffany Aching" books:
The Wee Free Men,
A Hat Full of Sky, and
Wintersmith (particularly the last, given what you've said about her, but the others are excellent as well). Also Garth Nix' Abhorsen Trilogy:
Sabriel,
Lirael, and
Abhorsen. I believe all these are available as commercial ebooks.
For manga, I recommend
Fushigi Yuugi -- lots of angsty teen romance with nice guys (and some not-so-nice guys).
I don't know if it's available (legally) in ebook form, though.
Ah My Goddess would probably also fall into the "nice guy romance" category.
Sailor Moon, of course, is a classic, but she's probably already read it, since the series ended years ago.
Ranma 1/2 is a romantic comedy. Actually, anything by Rumiko Takahashi is likely to suit.
A few ideas to get you started -- how many books were you planning on buying?