if you're going to argue that, it really blurs the line between "physical" and "mental" to the point where nothing really makes sense anymore. honestly, i don't have a problem with bella being immune to kate, since she's already been shown to be immune to jane, and kate's powers are basically the same as jane's, other than requiring physical contact (and she's been shown to be immune to "mental" powers that require physical contact, with aro). it's completely silly, but there's at least consistent internal logic there. it would actually make LESS sense if bella weren't immune, since that would suggest that kate is actually somehow conducting an electrical charge over her skin, which 1) is stupid and 2) would make everyone's reaction to benjamin very confusing.