It's hard for kids to grasp the idea of a time until they are older. I'd let it go...she'll eventually get it. My 4 year old niece sometimes gets it, but then will sometimes make comments about her being there when I was a little girl. I always just say You were there when I was little?! and she says Yes! and I just say Wow, I didn't know that. And we move on. Hope this helps!