Who is Layla? First time playing

Hi,

I just bought Origins on my new xbox, i'm confused about Layla:

Who is she? I've had multiple scenes where she wakes up from some kind of dream and talks about memories, memories that i play with Bayek and Aya.

As far as i know the action takes place somewhere BC, and it's about the beginnings of AC Brotherhood but what's the thing with the dreams?