Lots of great recommendations so far. I would add:
-Anything by Nancy Farmer, especially her Sea of Trolls trilogy, which is a coming of age/wizard-y series that uses Celtic and Norse mythology.
-The Percy Jackson & the Olympians series. These are super popular amongst the grade school kids, but not super trashy. It might also get her interested in Greek mythology.
-Linda Buckley-Archer has a trilogy that for some reason has different titles for England vs the US. Look for it under either the Gideon Trilogy (First book is Gideon the Cutpurse) or the Time Travelers Trilogy (First book is The Time Travelers).
If she's into current fantasy series, I'm sure she'd like the classics: The Dark is Rising series, Chronicles of Prydain, A Wrinkle in Time, etc.