There's no evidence that most people hardened her. Given that people tend to favor 'good' choices, I'd be comfortable betting that's not the case.
When has Leliana NOT been a religious fanatic?
Always.
I was wondering what became of Leliana? From the marketing materials so far she seems unapologetic, harsh, cold and religious fanatic. Its the vibe I'm getting from the character.
What changed her? The image I had in my mind since Origins was this humble servant/believer of Andraste. A little broken character, turbulent past and all.
Is there something I'm missing here, like some optional DLCs, books or other satelite lore that alters her image inbetweex the games?
Yes. The game begins at a peace summit where the Divine and the heads of the Chantry get blown the hell up. If someone destroyed the Vaticin tomorrow, murdering the Pope and the College of Cardinal, you can bet that many Catholics would experience shock, grief, and anger.
And Leliana is even friends with the current Divine. She's the women who helped her escape the dungeon after Marjoline betrayed her, and Leliana has spend the last few years working for her as the Left Hand of the Divine.