Since we're talking hypothetical, I'll throw one out there.

First I would change the acquisition of lillies so that they
1. Grow slowly while in combat
2. Gain the next lily (or add progress of one full lily) when using water-aspected spells/abilities.

Then instead of the shield ability, I'd add Bubble (however they have to tune it up to 2x hp buff) as one of the water aspected abilities. Fluid Aura could be one of the others (leaving damage on the skill so you'd actually use it).

Then I'd have a single skill to consume the lillies: Summon flowers. It would be a ground aoe you put down, 1 flower spawned for each lily in your bar. They could grant some buffing effect for 15-20 seconds, and apply a debuff on nearby enemies when they expire.