Her hair glows when she sings, yes, but only when she sings a specific song, which is the Healing Incantation.

Flower, gleam and glow
Let your power shine
Make the clock reverse
Bring back what once was mine

Heal what has been hurt
Change the Fates' design
Save what has been lost
Bring back what once was mine

What once was mine

It only glows to this specific song, not any others.

Yeah, I know. MovieMistakes made a mistake!

Yeah I noticed that too. I know its kinda bizarre but it only glows when she sings the flower gleam and glow let your power shine make the clock reverse bring back what once was mine song which makes her blonde hair glow(but once Eugene chopped it off and it turned to brown her tears brought him back from the dead). You need to watch the movie if you any of you didn’t get the chance to see it yet.

exactly and btw it's called Healing Incantation