Looking at default functions, I only see
IncrementRemainingFeatUses
DecrementRemainingFeatUses
DecrementRemainingSpellUses
So I'm pretty sure you need a plug-in or something -- though if you made it a feat and could get her to use it via scripting that could solve your problem. Could possibly do it with PlayerTool1 or something -- basically adjust the spellcasting AI to make it choose that feat over a spell if no other spell remains. PlayerTool1 has no cast time or anything so that might lead to odd results, though.
If you wind up making a custom feat, then making a "generic" spell would be useful -- make it medium range, requiring a specific target, and no projectile visual. Then you could use that for a bunch of different monsters using your own spell visual and effect based on the casting creature.