Why was Yoshimi killed?


In the second part of the series after the first time skip, Saki learns that
she did have a sister called Yoshimi. According to the comments made by her
mother, Yoshimi was killed by an Impure Cat.

Yoshimi showed signs of having gained her powers early but didn't seem
controlled because of how her name looked in the mirror Saki found.
Considering that she didn't look all that much older to Saki,

  * Was Yoshimi really that much of a threat to have developed her powers so early that she had to die?

  * Isn't the purpose of the Unified Class to help children and teenagers control their powers? 

  * Why couldn't Yoshimi just be a child prodigy who could one day take Shisei Kaburagi place? 




There's an answer in the book. She had an eyesight problem (astigmatism +
short-sightedness) that was misinterpreted as a defect of her cantus. Her
eyesight problem is the reason her name in the mirror looked the way it did.

