There are reasons in game and easily found out about some of her seeming wishy washy ness, especially concerning her and Le'azel. I'd ask that you simply start a new character and play until you meet Shar. That should clear up some of the confusion if you pick the right things.
As for her other back and forth. If she is neutral evil, then she probably doesn't much care treating animals kindly, or it could be she likes animals, dislikes people. She doesn't mind doing things if there is a benefit to her. She maybe having a crisis of faith do to something she's seen, or had to do, which has left her bitter. She may very well have a depth of character that most characters in video games don't have. Until you try everything at least once, you can't really have the full story. Even changing a race leads to further enlightenment on the first time you meet her. Changing who is in your party triggers a back and forth that gives more details, or leads to revealations about her, and even the others.
She is definitely evil more often then not.
Of course, Shar is not Llot, most likely SH and should be mysterious. But her motives and theme Shar needs more disclosure in the game.
So far, SH does not look clear, neutral
Compared to the cleric of Llot SH, she is not only good, but generally a saint
Why is it so frightening to everyone that she is a cleric of Shar? It is not clear.
Is she really happy to be Shar's cleric, or is it self-hypnosis? It is also not clear.
Need answers in release
Shar is an evil goddess which is why it's bad for her to worship, they don't do nice things at all, which leads to their frightening of others. Believe there are lore drops in game you can find that tell some of the story, even conversations with Shadow reveal some of the things she's either done or has seen done, or been trained to do.
Some of the unclarity begins to take shape through different playthroughs, and conversations, party comp, etc. Little by little details are revealed not massively, and not all in a single playthrough, or by simply playing a single race in each play through.
