Lavellan also speaks in elven to another Dalish, in the amulet quest. You could probably rp it however you want. I think she understands and I imagine she'd ask him later what that was all about and he'd deflect it, saying the demon was just taunting him. I mean, now that I see all the signs, I can't believe Lavellan doesn't at least guess that he's an ancient elf.
I wonder if she ever tells the story of Fen'Harel around the campfire like Merrill did. Awkward. Though the wolf has very different symbology in the Emerald Graves, something else I'd hope that she'd notice.
Yeah, it does require some roleplay. Roleplay is also needed due to how Lavellan constantly uses Andrastian terminology, even when meeting the Dalish in the Emerald Plains (I suppose it's to avoid confusing Andrastian companions who might confuse 'shemlen' for the derogatory slang term 'shem', or who might be confounded about what 'the Beyond' is).
As for telling the story, I really like the sound of that. I'd imagine Lavellan might share stories, especially when other Dalish start heading to Skyhold.
It could be that the script is lost to them. In Witch Hunt DLC, Finn can read elven tomes that a Dalish keeper can't.
Well, Finn had access to elven tomes that were taken after the fall of the Dales, which is why he knew the word for 'Eluvian'. Although given how Merrill had access to lore about the Eluvians, I suppose it varies from clan to clan.