So riots current fix for yummi was a numbers hotfix with around 10 buffs but the problem wasn't just numbers but a design oversite on how her passive should work with her kit.
The below suggestion is how I would have changed yummi before a numbers change to not only offer a more coherent feel to her kit and play style but also to give reasons to think about her spell leveling path a bit more.
How to fix yummi.
Make it so if yummi lands her Q on an enemy she can AA it from much greater range (similar to how caitlin traps work) but have it scale off Q lvl.
Example if yummi lands her empowered Q on a target it also increases the range yummi can AA that target by 75/150/225/300/375/450 range for her next auto attack on that target or the duration of the slow, whichever occurs first.
This lets her more safely apply her passive for the shield while still offering plenty of counter play like blocking it with minions, dodging it, the tank taking it for the carry, exc.
I think this would have been better than a raw numbers buff for fixing yummi.