the fact she's using what seems to be an offensive cantrip argues against it (not strongly since there's technically divine lance, but it's referred to as a ray...I'd bet Ray of Frost, pegging her as a Primal or Arcane caster).
"The power stirred a surge of dark glee in her heart, and she laughed, the laughter spurring her ray’s power longer and harder."
This quote specifically mentions it being sustained by Cackle (which we now know is a feat), so it's probably a new sustained damage spell or hex. It does sound like she is either arcane or primal, though.