This is one of the things that bothered me about Breaking Dawn- when the vampire powers stopped making any sense. Edward being able to read minds makes sense, you can understand how that would be a useful power for a vampire. Same thing with Jasper controlling emotions. That’s all very vampy stuff. Kate’s ability to shoot lightning out of her hands (or all over her body) makes no sense. In what situation would that possibly be useful? It’s not like she’d need to use that power on humans ever and we’ve already seen in ‘Eclipse’ how easy it is for vampires to defeat other vampires in battle- they run at them real fast & rip their limbs & heads off.