Bewitching Season by Marissa Doyle (2008)
I heard about this book from the YALSA listserv. It is a by a first-time author, and I feel it is very well-done.
It is unlike a lot of other books with fantasy themes. Magic exsists, and amongst the well-to-do families of London in the mid-1800s, when Queen Victoria is about to take the throne. Twins Persephone and Penelope are witches, but no one in society is to be made aware of this. They are also being presented out in society, with the hopes of making good matches for husbands. Their neighbor is also grown up, and showing much interest in Persy. Pen is much more interested in society, while Persy is extremely nervous and upset by the prospect of balls and dinner parties. Meanwhile, their teacher/nanny who was also teaching them magic on the side (and their mother supposedly doesn't know) is now missing, and the two young women are having dreams about where she might be.
This is a well-written book that I highly enjoyed because it brings historical fiction, fantsy, romance, and some mystery together in a fun way.