According to 12 year old actress Joey King she says she is playing a young version of her. As she states.
I play young Talia al Ghul. I can't give too much away because I promised Mr. Nolan I wouldn't say anything. There are too many secrets about the character and the movie.
So it seems that Marion Cotillard could be playing the adult version of Talia al Ghul for those who don't know is the daughter of Ra's al Ghul and the mother of Batman's son Damian who is now the current Robin in the comics books.