that's what's so contrived about it. Apparently religion checks are a thing until they aren't, because our tsundere girl needs to have a big secret and reveal
This is a big part of the issue:
Larian love their mary-sues, and wants to let them break the rules wherever it suites them. They don't WANT the player to make the sorts of rolls or checks they normally would in any situation involving one of their Origin characters, because they're desperate for their origin characters to always have the upper hand and the last word against our PC. Nearly every situation involving an exchange between the PC and an Origin character, the PC is forced either to be incredibly dumb and say incredibly dumb things, or to be ignorant of what the Origin wants to talk about (without any knowledge checks offered), or else they have to say directly conflicting lines without any tact or sense, just for the express purpose of allowing the Origin character to springboard of the line into something more condescending. The vast majority of all PC-Origin dialogues are written this way, with it only starting to wind that in a little bit on SOME of the advanced relationship dialogues later on.
==
While Shadow's in game armour doesn't have the same Shar regalia that her splash art does, her circlet is another matter. It's a simple diadem with a flat, perfectly circular black onyx as its sole decoration, and in terms of the forgotten realms, it is very obviously a symbol of dedication, not mere ornamentation - and can only be a symbol of Shar; anyone should be given a check to recognise this upon seeing her wearing it. You can add her hair piece to that - it has a bordered black disc icon as its central focus, as a clear symbol that matches her circlet. Between those two alone, it isn't feasible that anyone would fail to understand it as deliberate symbology, and only someone in *extenuatingly* ignorant (which our characters are not) circumstances should be denied a check to know what it is.
==
Part of a narrator's job is to fill in the gap between what the character would know, and what the player might not - theirs is a tool to inform the player without implying ignorance or stupidity on the character. A not insignificant part of DMing is doing exactly this, in fact... and it should be done here.
