How to nerf Zoe
Well, here is an idea, do NOT nerf Zoe's damage, but have it so that her abilities use more mana, make sure she has a lower mana pool overall and maybe even consider her ult scale in mana like kassadins ult. She could still have that one shot potential, but at least she won't be able to spam her abilities. Also consider there being a cooldown for her spell thief ability after using it. I think nerfing her damage would be better BUT she could probably just end up one shotting a squishy anyways so this is probably just an alternative.
EDIT: Also maybe make her sleepy trouble bubble a smaller skillshot, making it a bit harder to hit since its a really strong ability.