Well, even if this ends up being the case, if during the time she's been a Sharran she has done evil things, she's still guilty of having done those things, isn't she? Innocent people suffered because of her actions. Why should the slate be wiped clean? I just don't accept the idea that if you do evil things but then later on express remorse and "repent," that's all it takes for you to be absolved of your evil actions.
This could turn into a philosophical debate but anyway, it actually depends: if you are doing things because someone is mind controlling you (and in D&D that's a distinct possibility) you are definitely not responsible for your own actions.
That said I do think Shadowheart is on some kind of terribly evil mission on account of her masters and she's responsible for her current actions although she's probably got some mitigating circumstances. I also think the player will be given a chance to redeem her, thwart her and her masters or join her in evil.
P.S.
The idea behind redemption arcs is a character/person realizes his or her mistakes and TRULY repents (not "repents" then), asks forgiveness and then does his/her best to make good on his/her mistakes (which entails penance as appropriate). This logic is actually rooted in a lot of the western legal systems. The idea that if you do something wrong you are automatically a rotten and irredeemable individual and cannot find forgiveness is pretty terrible and unsustainable if you think about it.
