When the F&*! Should i pick Zoe??

FOr some odd reason most of the time when i get REALLY fed my team feeds out of their asses so carrying becomes very difficult. I guess this is coming from a cassiopeia player (If you're fed enough with her you can carry a team easy,) and vise versa ( when i feed out of my ass.)

When do you pick her? She seems like a safe first pick (as long as zed is banned) fizz is really god damn hard but you can at least farm safely and roam. Im not sure, she doesnt seem like a hyper carry, and her aoe is lacking.. I really like her help???