Honestly speaking, Rowanna seems to be not so great of a unit. I mean, while status immunity is nifty, it is also niche enough to play around without it, and without it she is just a yet another duelist. Class gimmick may sound good on paper, but is rather tricky to use, as if you drop her with your main forces, in vicinity of a healer, she will almost never activate it due to being topped off all the time.
I guess she could be used as an forward detachment unit, operating all alone, only sustained with her own skill to maximize the time she spends with her multiplier active, but you will need to babysit her health constantly... And she won't get to solo bosses that way anyway)