About Selena's ghost writer/singer : yes, officialy she (Julia Michaels) is just her ghost writer. But, when a ghost writer makes a song, he makes a demo with it. This demo is just for the singer, but if you hear closely Selena's songs, you can recognize Julia's voice. They kept Julia's voice in her album, for high notes, and chorals, in a lot of her songs. Yes, Selena doesn't even write or sing her own songs, in her own album.