Crowea's buff is a self buff, but that I can see why it's confusing based on how wikia worded it. It's written as when any party member drops below 50% health, increase Crowea's own atk by 50% and dmg by 35%.
However, I can definitely see sacrificial buffers setup working out with Cardamine as triple self negate and guts will keep her alive for a while. Just fit her with crit buffers instead, as well as Pierce based memory or 6* Skill/boss dmg memory in the party.
On the topic of sacrificial buffers, Montbretia has 2 party member atk/skill dmg/boss dmg buffs which may appear difficult to use on first sight... but when you only have 1 girl standing, it will work out very well. So Let's say if Cardamine is the only one alive, then her buffs will always go to her.