The forest sings sorrow, seeping through jugs of sunshine and leaves. It’s the infectious kind of sorrow, different from the kind of misery that draws company, and instead radiates from the inside out like the ripples formed from a dropped pebble in still waters.
Or perhaps she was feeling down before entering the forest, her heart full of foreboding simply from thinking too much about the course destiny has set for her. There’s something prison-like about words like “ever after” or “forever”, and it makes her want to do everything right, as if each little thing matters more than gravity.
So her song turns into sorrow, so much so that even being caught in a cage won’t make much of a difference.