Guys. In Forgotten Realms, on Faerun, gods and goddesses are real and very active. Their symbols and statues and lore are everywhere. You are talking about Native Americans who were isolated from eastern cultures and Africans who were also isolated, and you are talking as if the general populace of the Sword Coast region is the entire world of Faerun.
Yes, there would be pockets of people in Faerun who have never heard of Shar. Yes, absolutely true, but not in the Heartlands, HEARTLANDS mind you, of the Sword Coast halfway between 2 very popular and populated major cities that all believe in the same Pantheon of Gods. Shar and Selune were and still are when the game takes place, VERY active goddesses in the entire region.
In the Time of Troubles, back around 1358-1372 DR (can't remember exact dates right now) when Moonhaven was destroyed, Shar and Selune literally came to Faerun in avatars, and they flipping battled in the streets of Waterdeep for everyone to see.
Now, in the game, it's been over a hundred and twenty-ish years since then, but these goddesses are still major figures in the entire culture of the entire region.
So, it is more like someone from Ancient Greece who lived in Ancient Greece their whole lives, not knowing who Hades or any of the major Greek gods were. Imagine someone in Ancient Greece seeing a symbol of Hades and saying, "Hmmm. Oh well. You're a cleric of who now? Nah. Never mind. I don't wanna know. I'm not interested."
I don't think that it's unreasonable to ask Larian to put in a Religion check to see if your character recognizes or just even questions her outfit, if they are going to still have her roam around in that outfit. My personal preference would be that they would not make her so stupid and that she'd at least not have big black orbs on her shoulders and a huge circle on her chest and forehead. Just tweak the armor to not scream Sharran, and have the character ask her what her religion is when they first meet her on the beach. She can lie through her teeth, and an Insight roll made by the MC could detect that she's totally lying, or if you fail, you just don't realize that she is.
She could say, "I serve Melira Taralen," who is a goddess of deception that is much lesser and much more accepted than Shar if people even know her at all because she's more unheard of who is also of the trickery domain... or someone similar. Thus, she can explain away using her trickery domain powers without making it so obvious that she's a Sharran.
I would even use the same armor, but have the black orbs missing as if the armor was damaged. She removed the stones to hide who she really serves so no one would suspect. However, once you head into the Underdark, a small cutscene shows her putting them back on along with the big black circle on her chest. "These will enhance my armor and provide Shar's blessing upon it," she says. "Now that we're not going to be roaming about on the surface, I feel safe putting these back on." Then her armor provides her with some sort of Blessing of Shar or something to make it special.
