100% she's a bigger threat.
She's competent and calculating where Rua's impulsive and petulant. And I would bet my lunch money that she is fully invested in getting him back into the family fold, because even if he weren't Rua's fiancé, he's a super powerful asset that she put her own time into training and developing.
And of course, also because she would still be beholden to the patriarch - there's a chance she personally would let him go free, but doing so would anger the Grandfather and she could be finished for failure.
And I don't know if I'd even believe she would personally side with MC; nothing about her thus far says she even feels differently than the Family, so.
Plus - she trained MC. I assume this means she's as capable as he is.
