I think you should work on adding chalice as a first or second item. Zyra is very slow/squishy, mana dependent, and has high cooldowns, so Chalice helps provide some defense and utility which she desperately needs (unless of course you are against AD, then rush armguard + morello).

Also since you will get sorcs and haunting guise as 2nd/3rd items, I don't really see a need for MPEN quints. AP quints will help more with early trades.