User blog comment:Gundam Legilis/Music of RWBY/@comment-10380701-20150816133303/@comment-26882656-20150816140045

Given the White trailer's questionable canoninity she might not be a singer. For all we know the White trailer was all in her head. A mental landscape if you wish. A remix Mirror Mirror does appear in the Yellow trailer but... so do Red Like Roses and From Shadows.

What kind of scenario can you think of where she would sing? An opening ceremony for the tournament perhaps. (Where Ruby just stares starstruck at her.)