Cool concept.
You've got some nice specifics. Maybe too many. ;)
I'd start with your protagonist and give her one goal. I feel like she's got 2 goals here: a) success (I figure it's 'success', since she's determined in some way) and b) rivalry with her former bandmate.
So, start with 'A determined singer must GOAL or else STAKES'.
Or: 'A singer's rivalry with her former bandmate leads to tragedy when SHE DOES SOMETHING TERRIBLE'.
The theme sounds like it might be greed versus humanity, or similar? The theme itself might guide which goal you choose. And so will the tragedy -- if it's at the start of the story, then it might be an inciting incident, and worth mentioning. If at the end, then you might not want to mention it in your logline -- let the suspense unfold as it may. :)
Keep us posted!