Critical and weakness teams deal the most damage. You need a weakness girl most of all, and you dont want to be starved for skill act.
Id look to get Pygmy Water Lily, or Sakura SS for weakness(if you can compensate for the slowness), if you can get a team to 80% crit rate with 4 girls, then you could use Fennel yukata or Sensitive plant.
For Kerria, Id put her on her own team and RG Hydrangea for the biggest impact. Get Cowslip maid or another per turn damage girl. Since you have H Peony Hw put her on that team for some crit. Try out that setup and I think you will be pleased with the improved performance
Edit
Anyhow, I like reaction best so I like the event girl. This is what I am building should be ready in a few weeks:
need more skill flowers to install cactus for additional power if needed. Team puts out 210% Crit damage and has three re-act girls.
Have good sub for Cactus meantime with the 1.36 skill act until the team skill act is ready (RG Fuchcia and she does re-act too and has skill dmg but no crit).
Each girl needs to have at least 35% to run Cactus and with the new FM she will be at 90% re-act