Even in previous versions when you can't free her, she still shows a bit of appreciation when you've tried. In general, from what I've seen, outside of her deep hatred of Giths and Selunites, Shadowheart can be somewhat pleasant.
Yeah, even in previous versions, she reads as a basically decent person who has been fed a load of BS on Shar, Selune, and the like.
Which, to be honest, is par for the course with Shar. That's a goddess with a long history of luring people in and chewing them up in a way that has her victims saying "thank you for devouring me / ruining my life"... even other gods.
Seriously? Why should I (in game) care about any of this if I'm a good-aligned person? If you're a priestess of Shar, by definition you are NOT a decent person.
Let me ask you this. What if the game allowed my PC to say to SH: "Your so-called goddess is an insane psychopath whore, and if I ever get the chance to lop her head off I would do it gleefully." What would SH's reaction be? What would my PC's subsequent relationship with SH be?
If you are even a mildly good-oriented PC, and you are ROLEPLAYING your PC properly (which is to say, true to the nature and lore of the setting within which your PC exists), SH should not be "savable" or "redeemable" simply because she should not be in your party in the first place. In fact, it may even be the case that she would be dead.