If I Was Your Girl (by Meredith Russo)
This is the story of Amanda, a girl who moves in with her father after a Difficult Past and starts over at a new school. And the story hangs largely on her narration and characterization, as Russo explores her inner conflicts and her negotiation of relationships while learning to live as herself for the first time in her life. What Russo has done here is not only make Amanda a wonderful character you really root for, but also has given all the secondary characters -- who sometimes get short shrift in YA novels -- full inner lives and story arcs of their own. I loved that.
At heart it's a YA romance -- Amanda falls in love with a boy at school, but will he still love her once he learns her secret? But it's a nuanced examination of what it means to be a trans girl, the good the bad and the ugly. I read this book in a day (could not put it down) and cried through the entire denouement.
I particularly appreciated Russo's author note (where she mentions she herself is trans) because she acknowledges some of the more "fairy tale" aspects of Amanda's character and explains why she made those choices. It completely worked for me, as a cisgender reader -- although if I were a trans reader or the parent of a trans child, it might work less well, I can't speak for those audiences. From where I'm sitting though, I think this is not only an Important book for teens to read, but also a very well-written one. Really, really great YA.