"I was born fully grown so there wasn't any need," Billie lies blatantly in response to that question. She's fairly adamant to be as unhelpful as possible, especially on this topic. Strange isn't a shiftling and he's done nothing to imply she should trust him, so that makes two people unwilling to lose a battle of wills here.

Anyway, she pushes away from the rock and goes to fetch her coat, to pull that back on as well. Doesn't mean she won't keep talking, though, because she shoots back, with, "What about your ears? Were they that size when you hatched or do you elves grow them pointy later in life?"

Yeah, she knows elves don't hatch. She also knows, yes, they just have ears like that, but she's intent on being an asshole about this.