I got that vibe as well when going through the voicelines, but it seems to me that the Nightsong is posessed by Shar when she's saying the pro-Shar lines. The tadpole breaks this posession and then she start saying the panicked anti-Shar lines, until she is taken over again.
Also yes, Shadowheart is not even a person anymore at this point lol, just a tool the Sharran cult of BG uses to get the Gith artifact.
The lines I'm talking about aren't in the voiced lines and she doesn't appear to be panicking. In case 1, the Nightsong is telling Shadowheart that gaining back her memories will anger Shar. She plays on SH's insecurity quite a bit. In case 2, the Nightsong is encouraging Shadowheart to remember because she is meant for greater things and to follow her "destiny". No warning about making Shar angry.
There is another person who talks about Shadowheart's great destiny: Ketheric (Chosen of Shar). Shar told him about it...
There is one thing that can reconcile the two, Shadowheart brings up Shar testing her. Case #1 is the test, case #2 is when Shar is pleased by the result.
and I don't think she is a "puppet", well not anymore than anyone who worship gods in the Forgotten Realms. lol.
