On Ivy, while she is mortal you could definitely argue that it's sponsored magic, or that the magic is innate to her and flows out naturally and unconflicted rather than the wizards conflicted brute-force approach. Or it could just be that her knowledge of magic is so advanced that she doesn't suffer from the hex effect, either because it just doesn't happen, or because she's learnt to ground that extra energy instead of allowing it to cause havoc with the laws of reality.
I think the obvious rule is, no matter how it happens, it is possible to take steps against hexing equipment but that it can always happen no matter how old or uncomplicated the technology is. For accidental hexing, the longer the technology is around magic the more likely it is to break down (with more advanced technology needing less time to break). For deliberate hexing, any complicated piece of equipment can be hexed but the simpler and more reliable the technology is, the more power it takes. With enough power you could probably hex an abacus, but it'd take hell of a lot!