Depends on how we interpret it. Techbane isn't an emp or something, it's the bane you accept for practicing magic. Not quite paradox, but the same zip code. The trigger isn't magic being generically bad for tech, it's mortal magic making tech fail in ways inconvenient or dangerous to the people around it.Given the complexity of a nuclear device, I would consider techbane causing a detonation to be quite unlikely. A fizzle maybe, but even then… At least for modern implosion type warheads.
A very complex failure isn't necessarily any more unlikely than a simple one for the same reason Harry can track someone with their hair without doing a gene comparison to everyone in the city in his head. Magic doesn't necessarily interact with material properties or information under their normal logic.
To draw from canon, Harry's tech bane is equally capable of making a high tech modern gun explode in his hands as it is causing the electronics is a car to start looping the same warning audio constantly. Which is a very specific and weird problem to have if it was a uniform field randomly applying the same pressure to different objects.
If it was doing that I'd expect the electronics to just fail entirely.
Maybe, but if they're heavily indoctrinated then simply making them hate her wouldn't necessarily stopped them from doing what she said.May I say that all these phones calls would have been a great opportunity to use Golden Years tainted black. Basically could have ruined Sandra's relationship with all her pawns and considering how her relationships seem to have been built on mind magic it feels like just undoing her influence. Would not have even cost us any essanse.
There's also the consequences for the target. We don't get driven crazy by altering someone's mind like a wizard would, but the mortal is still a mortal.
My base assumption is that unlike regular mind magic our charms don't implicitly drive you crazy the longer you're subject to them and the deeper the change they inflict on their own, but I'd be concerned about the health of someone who's got a solaroid charm twisting one way and black magic twisting the other.
In the charm-brain-spell wrestling match I think there are good odds the weak link would be the brain.