It feels to me like every story of the Dresden Files has a positive note in there. This tends to render most metal songs a bit unfitting; they tend to the dark side.
Likewise, any actually positive song is out (as a story themesong) because the stories do tend to have the negative side too.
That said, there's no reason to ignore them for personal themesongs!
For Molly after Cold Days, I am partial to Oonagh's "Märchen enden gut" (fairytales end well). The German distracts a bit as Molly is certainly not German, but the sound and essence seems to fit to someone who is holding on very hard (and possibly failing in the future) to the idea that even through the bleakness, fairytales will end on a positive note.
Alternatively, Frozen's "Let it go". Not nearly dark enough for Maeve, but Molly "unchained" would fit with the song.
For Mother Summer/Winter, I'd go for Celtic Woman's "The Voice", with a upbeat sound but also such gems like "I am the voice of your hunger and pain".
For Mab, Within Temptation's "Ice Queen". Should be obvious enough. Though it could be applied to Mother Winter as well.
For Lasciel, Within Temptations "Angels". Again, pretty obvious - it is all about a false saviour of a fallen angel. But it has the deception angle too - this is not an obvious dark angel like many of the Denarians' partners, it's a seemingly helpful angel who turns out dark (and who gets a proper kicking at the end of the song).
For Butters, Prince of Egypt's "When you believe". The realization circa Skin Game's end that, indeed "who knows what miracles you can achieve, you will when you believe". Plus a bit of Hebrew thrown in for good measure.
For Uriel, Prince of Egypt's "through heaven's eyes". Nothing says Uriel quite like this song's sense of: in the big picture you're doing great, but sorry, you can never understand quite how.
