Dance of Shadows by Yelena Black
Vanessa stumbled out of step. The figure beside her froze, her face twisted with terror. Vanessa watched, horrified, as the girl jerked left, then right, her body bending like rays of light refracting off a mirror. The glare engulfed the ceiling. Vanessa covered her face. The last thing she saw was the outline of the girl's lips, pursed open as her figure ripped into a blinding curse of light, the rays streaming from her mouth like a scream. - Page 226 (ARC copy so teaser may differ to the final copy)
This book started off a bit slow but very mysterious and now it's so much better I can't wait to find out what is actually going on.