If you want to stick more or less to the rules as written, you'll probably have to ditch the stress-track-clearing idea. Maybe create Aspects that can be tagged to cast spells without stress instead - that at least has some precedent in sponsor debt.
The main problem with that is it's 3 shifts to create an aspect, so a 4-shift effect would only give one aspect to tag, which is one spell; at that point, you're better off just having an enchanted item that is, itself, a spell (though I suppose I could convert one of those shifts into an extra usage).
I've looked at how the RAW handles things like Harry's super-coffee potion and the bear belt, and they don't seem to
quite match the effect demonstrated in the books; the super-coffee potion acts as Armor:1 against stress from calling up power (while retaining the 1 stress minimum) and lets you ignore fatigue consequences (they still exist, they just can't be tagged or invoked), while in the book it seemed to recharge Harry and give him extra energy he didn't have before. I don't have the Paranet Papers on me, but I think the belt was similar, in that it mainly worked by suppressing already-existing consequences, though I'll have to double check it.
Edit: Double checked, and yeah, the bear belt buckle just lets you ignore tags and compels from up to two consequences, which doesn't quite fit the rejuvenation Harry describes to me.
Setting aside the RAW, I like this option:
Might be a bit problematic if it was in a book, but it sounds like a good idea for a group where nobody's gonna try any shenanigans.
What potential potential shenanigans do you see with it?
My fear with Option A is how well it would scale in the long run. This is a powerful enough trick that you dont want them to be able to just shrug off the "attack." Id want to ensure that there is some downside to using it regardless.
That is a good point, it would be less dangerous for higher-level wizards.
That said, it's potentially an 8-shift attack (higher, if you're using PP's Mental Toughness powers), and I doubt many GMs will allow a Discipline score of more than 6. So almost by default, the defense is at a disadvantage, and if you're in desperate enough straits to use this, chances are you refilled most if not all of your mental stress boxes after using the item, in which case even a 1 or 2 shift hit could be a take out or consequence.
You could use a fate point to boost the Discipline roll; and if your stress track is still clear you could be okay; but if you had fate points to spend and didn't cast spells after using it, why would you use it in the first place?
One way to mitigate the overlap when the stress comes back is to treat it like spell Backlash, so that she can choose to take it as either mental or physical, and thus she has the option to leave her mental stress track open for further casting, if thats a concern in a given situation.
That could be an option, yeah. Though it could be an easy out if you haven't taken much physical stress. I feel like there needs to be, if not a certainty, then at least a reasonably high probability of ending up with a consequence or at Taken Out as a result of using this.
Haru: I'm sorry, but the consequence thing just doesn't seem to fit for me and it doesn't feel like it scales well with the enchanted item rules. Imagine the item applied to physical consequences, for instance, and a more powerful mage -- I've had some who could crank out 6-shift items with 5 uses for one enchanted slot apiece; under this scaling, that's 10 additional consequences to dole out, which is insane, even if they go away at the end of a scene. Consequences work best as a resource limited by skill points and refresh. I just don't think they're in the purview of enchanted items.