Date with a girl and shes bringing her friend?

I have something like a date with a girl that I am looking at for some years ago and still doing that. I ask her for a date and she answers that she will go out but she will take her friend. And I accepted that because I think the girl needs opinion of her friend. My real problem is that I do not know what about to talk and how to become a good essment of her friend? pls hlp!