I was all set to suggest the original Sherlock Holmes stories by Arthur Conan Doyle, based on her preference for mysteries. Then I remembered that Sherlock was a cocaine addict, and can't recall how prominent that little character fact is in the stories. It's been a long time since I read them, and my memory is clouded by the Hollywood and BBC versions that have played it up. They may or may not be appropriate, I'm really not sure.
I thought of Jane Austen, also suggested by pp, but wondered if the romances would be considered "too mature". They are certainly tame compared to most teen fiction these days. It's hard to know what some parents will find objectionable.
Eva Ibbotson writes some charming books for tweens/early teens that are historical fiction - Journey to the River Sea, Star of Kazan, etc. She also writes some fantasy (The Secret of Platform 13 and others), so you may have to be careful if you pick her books.
Karen Cushman writes some really good historic fiction for young teens - The Midwife's Apprentice, Matilda Bone etc. about plucky girls who are making lives for themselves in medieval England.
How about some non-fiction? Something like Walden by Thoreau or some inspiring biographies (Rachel Carson, Georgia O'Keefe, etc.) Hmm, maybe not O'Keefe (affairs etc.)