>>47610454IRyS.
The way to ruin her on a personal level is simple; just have her singing voice ruined a la Julie Andrews. She's not well educated, not smart, lazy, her singing voice is all she has.
With that gone, and the way she keeps being upset over obstacles that she can't avoid, the depression will set in. And then she will lose that bright personality that might make her attractive as a result, which would mean she would not be able to have anyone fix her. Coupled with her inferiority complex to her sister, she'll sink even further down and the vicious cycle of self-hatred & self-deprecation will do the rest.