I hear some people say that Shadowheart spills her Shar worship wayyyy too easily
But that's kind of the point, isn't it?
She worships the Lady of Loss and Darkness, Mistress of Secrets etc. etc. Shar's secrets are worth dying for and all that
She doesn't need to tell you this. You don't even have to roll to get her to tell you this. And her mark hurts immediately after, it's clear that Shar disapproves/she's being punished for disobeying such a vital tenet. That thing hurts whenever she even remotely strays from Shar, and it happens a LOT.
She could have easily lied about it, or not revealed all the details. But it's like deep down she wants to be able to share these things. Wants to have someone to confide in so badly. She wasn't meant for this life, to serve this Goddess, and I think part of her, a part she buries so deeply both for self preservation and for her own sense of hope, knows it.
And hope! Hope has no place in Shar's teachings, she says so herself. But Shadowheart is a hopeful person. She hopes that by accepting Shar, she can find a sense of belonging within her cloister. She talks about hoping that she can become a Dark Justiciar, and that she knows her hope doesn't fit in with her teachings.
She desperately wants to fit in with her people, but it's so painfully clear that she doesn't, and she's punished for every misstep that could indicate she's straying. Her faith is a facade she uses to protect herself, and something she clings to out of hope. It's no wonder she spills her heart out to the first person to show her kindness and an open mind. She's starved for it!
The only lies this girl is good at telling are the ones she tells herself.