Conversation so far:
does hilary duff sing in raise your voice
Reviews of Raise Your Voice, while indifferent to Hilary Duff's acting performance, were critical of her vocals, a number finding fault with what appeared to be her digitally enhanced voice.
does hilary duff sing in the lizzie mcguire movie
Even though Hilary Duff played both Lizzie and pop star Isabella in The Lizzie McGuire movie, she did not sing both characters' parts.
who sang instead of hilary duff in the lizzie mcguire movie
Hilary Duff's big sister Haylie filled in and lent her vocals to Isabella.

Question: why
Self-contained rewrite: why did haylie duff sing instead of hilary duff in the lizzie mcguire movie