Check how other actors call the attack animation. Where you see attack for animation you change it to spell. You haven't found it for Nova actor because that animation isn't used by anything the unit does.
I've got her to play the animation now. However, after she does it, if I tell her to move right away she doesn't go into her running animation right away, and instead kind of slides along the ground in the last frame of the melee attack animation for a short bit.
I've tried adding an Abil.Nova.SourceCastStop - AnimBracketStopSpell to the list of events on Nova's Unit Actor, but it doesnt seem to do anything.