She honestly isn't even that bad considering she was literally being mind controlled by the Absolute in act 1. [...]
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She's literally a Lolth - Sworn Drow ???
They are "bad", i.e. evil, by definition.
And Shadowheart is sworn to Shar, and objectively, was brainwashed to commit atrocities too - on her own parents no less. Could make argument that she is evil and unless you intervene she will stay that way.
Please no, otherwise there would be nothing that is exclusive to the evil path.
Plenty of quest rewards require you to be evil. A whole companion, with hours of dialogue which their VA spent years recording should not be locked behind a single choice you make imho.
