The Doctor's Daughter

"I am part were cat, part Time Lord. When I was two, my mother was murdered in front of me by a Dalek. I stopped talking after that, and ran away from my father when I was seven. My father never knew why I stopped talking; he just assumed it was the effect of Mum's death. But it wasn't that.
My name is Melody Piper, the daughter of the Doctor. I can see ghosts."
****
Melody was forced to leave the TARDIS when she was thirteen for an unknown reason to her, but the Doctor insisted. Now Melody's seventeen, almost eighteen, and she's finally believed he's given up.
And then he returned, and Melody's not sure what to believe. Is this really him? Has he regenerated, like he claims? And why, why has he returned after four years?