Zoe's Q is already pretty balanced as of now, even though some may not agree. Zoe's Q is hard to hit without using her E first... Or if a minion gets hit instead... or if she misses by a unit or two.
Now, I think increasing the first cast of Paddle Star! from 800 to 1000 cast range would possibly allow for more damage output and mobility as well as room for mistakes. And decreasing the second cast range from 800 to 700 cast range makes Zoe have to deal with more chance of getting hurt.
Also, possibly adjusting the scaling from 0.66 to 1.65 AP into 0.25 to 1.90 AP, and distance needed to hit with 1.90 AP is 3050 range.
This allows Zoe to have to actually have to think a whole lot more about dashing, the distance, what stands in the way and how to get the full damage.
Zoe would have to sacrifice or take a flash to get off her full, maximum potential.
Her passive, being a free Lich Bane; is already pretty good.
However, if she could possibly get bonus range on her next auto when it procs, it could make it more useful.
Maybe +100 range when it does proc; making her have a full 625 range on her next auto attack.
But then maybe only +50, for her to have 575 range instead. Because having an AP Caitlyn AA might make people think she's unbalanced.
Her W is ignored for it's possible damage and only seen as a second summoner spell.
Allowing her W to proc on-hit effects and changing the orb damage into physical damage opens a whole load of new options on her.
Besides, she's already gaining the damage from More Sparkles! when she does hit with her orbs.