It seems rather challenging to romance Leliana as a Dalish Warden.
Realistically, the whole "Maker, Maker, Maker" would be a real turn off at least in the beginning.
And later, she congratulates you for not being a savage. Very tactful.
For me, it kind of works like DAI.The whole Sacred Ashes quest becomes their Road to Damascus episode. It opens their minds more. Compound that, say, with guilt from the origin story and they might welcome support from someone like Leliana. And Leliana teaches about Shartan, which is something only the Dalish do still. If you're not guilt ridden in any way though, and play it as self-righteous, I don't think it works. But if that's the case, I think you should hate Alistair and Duncan for being full of ****, let Sten rot, and kill Zevran.
It's not as neatly straightforward as a City Elf or mage, but in a way, it picks up where the war of the Dales left off. There was a famous tale of an Orlesian woman who fell in love with a Dalish, before the war killed the both of them.