Her passive and ult is a problem. It's where all her power is allocated. If you get fed on Poppy, you become a death ball that can 1v5 a team, get two kills and run away before the enemy team can do anything about it. The reason she can do this is that getting to that point in any sort of competitive play is near impossible. The only idea I have come up with is as follows;
Note: I'm using X and Y for place holders for ratios.
Passive: Master Armsmith
After activating a skill Poppy gains a shield (X Armor + Y MR). Static cooldown 10/8/6 seconds.
Poppy gains magic damage on-hit (X Bonus AD + Y AP)
Q: Unchanged, except for; When Poppy uses Devastating Smash on a minion or monster, 50% of the damage affects nearby enemy and neutral units.
W: Passive just gives bonus stats, no more ramping up. Active changed to; Poppy throws her shield at a target location, gaining significant movement speed when running towards it.
E: Unchanged with an added effect; If Poppy targets her shield with Heroic Charge she will slide on her shield for X distance, briefly knocking up all units hit and applying the full damage effect. (Might have to tone down the total damage since it can be AOE)
R: Fugitive: Grants Poppy 10/20/30% damage application for 8 seconds to a single enemy champion, marking the start of the chase and granting vision of the target. Also allows for one use of Diplomatic Immunity Revoked; Poppy pulls the target back to the start of the chase once per use of Fugitive.
I'll ask people to keep their flaming to themselves. I'm a fan of Poppy as a champion, she was my first main when I started playing. The idea here is to keep most of Poppy's identity while making room for buffs and nerfs so she can fit the role of tank, bruiser or assassin, not all.