I will not assume evil just because she's a cleric of Shar. She says about Shar "She took me in when no on else did" (echoing Viconia in BG2 who said more or less the same). That appears to be a perfectly valid and not particularly evil reason to follow a deity, as far as there is ever a valid reason to do so. And who's to say that her regard is unjustified? Is a goddess out to destroy all of existence incapable of caring about her followers? Is a goddess's evil all that there is to her? We would say "no" about almost any human, and Toril's deities are actually ascended mortals.
So, Shadowheart might not be brainwashed, but right. From her perspective, following Shar may appear right in a way we would recognize as valid could we adopt her perspective. With no need for any evil on her part.
Sorry, but all of this I very profoundly disagree with. And furthermore, based on longstanding FR lore about Shar, much of it is also simply not true.
