Agreed. She was caught by surprise when she was grabbed and taken by Tartaros with her dark guild destroyed.
She could be simply twisted, with not specific justification. However, that hasn't been the case in any villain shown so far. All of the villains that had this much focus and screen time were always one way or another fueled by some other deeper reason.
I think that she hates people who have friends. People who have bounds. And specially when those people take those bounds, use that power and manage to be stronger than her. She should be stronger because she has no bounds. That was clear in her fight with erza. She was endlessly frustrated when Erza took power from her bounds with her friends. And she couldn't believe she had lost. We can even reason that her father didn't show her love and we can even assume that all her life she has been taught to value nothing but power thus her aversion to those who take power not on their magic alone but their bounds and their nakama. I feel her true motivation was to gain power but when her guild fell to the power of "bounds", she clearly saw it was no the place for her anymore. And as such, she tried getting into another group which would cather to her aversion to bounds and feelings.
I think ultimately, Minerva in her core searches for bounds, for connections, for meaning. In the end, it would be nice if she, like juvia and gajeel, would "fall" to FT. I think it would befit the story and make it richer to understand her character.
