GamerXiphos points out that during the scene in the Legend of Zelda: Breath of the Wild where we see Calamity Ganon flying around Hyrule Castle, we can just make out Zeldas Lullaby, which leads him to believe that the disembodied female voice, belongs to Princess Zelda, Watch the video below:

The part you should watch starts just after the 9:30 mark, in case it doesn’t start there.