Everyone already say what I want to say. To wraps things up, she's very broken due to abilities sync well to let her stay alive and amp her damage as she recovers her HP. As much as I don't want to admit, she's better than even Saffron in the realm of rank S due to her skill that recover HP. Kurenai picture should gives you idea how god-broken she is.
Or not, I try using Kerria in debuff team but her team couldn't solo all the way compare to counter team, maybe I do something wrong, or RNGesus is cruel to her. Maybe she will do better in crit team since Nidhogg is multi-form boss.
Final verdict in short: S
Sorry for short and half-assed grading. She's great and I own her too but she still not seeing any action for now because they nerfed down Nighogg too much.
Skip Daisy because loads of works and I don't really like her.