You are not alone in this. My wife was the same way, and I had to explain. I think they assume you'll read the books, but that's not good for those who aren't familiar with the overall story.
Also, Shadowheart SCREAMS of being a Sharriite from the beginning. Her entire armor set and headband say, "Hey everyone! Look at me, a walking Shar symbol.". The big black orbs are Shar's symbol.
So it's not done well. There needs to be a Religion roll made as soon as you meet her if they're going to continue having her in that armor. Succeed and learn who Shar is. Even if you fail, there should be someone, like Gale, who says something and teaches you about Shar. They could then have Shadowheart lie and say she stole the armor from someone or something.
See I have a divergent opinion on this. We expect too little of modern gamers - where we don't give them the opportunity to research things on their own outside of the game environment.
Also there is a chance we will have an encyclopedia that discusses the Gods and their domains, goals.
But in this case, a simple google search will bring you to the Forgotten realms Wiki which explains about Shar and her history. Its one of the things I love about Larian - they don't do 'path-polishing' - that is they encourage player investment and thought instead of leading everyone by the hand.
Honestly it's a great opportunity to learn things on your own, OR ask your fellow players.
I am speechless at the level of dumb contained in this one post. Yeah googling in the middle of a story because the storyteller failed to explain themselves is galaxy brain writing level.
