About the title I think you should do you. If you think the new title is a better fit go for it. It's your story you write it best? I don't know something like that. You have probably noticed already but I wuv your book. Ok bye!
I think that the demon is a bit late in the story to be in the “details”. I would change it to: but then she discovered her brothers terrible secret, and has to learn to fight to stay out of his clutches.
On a Unrelated note,
I found a good story that is almost completely undiscovered. Its prety dark, but i like it a lot. Its called: everyday normal violence.
It's really interesting that you say that, because my friend wrote this one for me lol. Maybe it doesn't read like my voice. Metal and Magic was always the working title, but I'm leery to change it at this point as I've never seen anyone else change there...