Shadowheart is Neutral Evil, a pragmatic who doesn't have a problem with anything as long as it advance her goals and makes her gain power. If you don't believe me, use your tadpole and in the dream #2 post-conversation, pick "I wanted it all" and then the "which part you liked best" option. She wants power.
Power appeals to her in the dream but I she is also disturbed by its appeal. She is happy to have saved the grove, upset when it burns. She is happy when you save the girl from the hag -- which is not true to type and she's happy when you take on the quest in the first place. Again, why annoy someone dangerous powerful and potentially useful? A true neutral evil character would not care about the rescue, ignore the girl and find out about the cure -- as Astarian wants to do.
And she likes dogs. Evil people hate dogs. Fact! It's even in the terminator so we know it's true.
I can't decide if that post is sarcasm or not.
She's disturbed because it's coming from the mindflayer tadpole (or so she/we thinks).
For the Tieflings, my guess is that she sees herself in them: the Tielfings are unwelcome everywhere, just like the Sharrans. They have noting left, which would match her urchin background too.
There is nothing useful about a hag outside killing her and looting her house (hoping the rest of the her coven isn't around) and Astarion doesn't wants to be cured of the tadpole, he wants to find a way to control it.
