Like I said, keep her on path of desperate power grab (due to her utter insecurities and fear after Orin has tormented her with processing her subordinates for food/tadpoling them as Minthy was unable to do anything at all)/revenge on her mother/Lolth or help her accept her surface life as a new beginning/be better than her filth of a matron mother has ever been. It's all the matter of perspective, really.
Not saying she should turn from evil to good like Sarevok could've done in BG2, but at very least become of lawful neutral alignment.
Even die hard Drow are capable of some good. Her family already has an example in Liriel Baenre who is currently a cleric of Mystra on surface.
Comparing Minthara to Viconia is incorrect in my opinion. One was infected against her will other betrays/leaves her people for own interests (worshiping Shar). In first case it's just the same person as it was in the underdark who's life was destroyed by cultists. But Viconia made her choice realizing consequences so her mind is definitely more open for changes what you can't say about Minthara.
