I doubt it's that ANBU girl..The one from Kakashi's picture of them and the Fourth shows Rin's eyes as being rounder and larger than the ANBU girl's eyes. Also, the ANBU girl's face is a bit firmer and not as rounded as Rin's. Then again, Rin's round face could have changed slightly as she aged and grew out of her childhood. Even with that being said, however, it's unlikely that the ANBU girl is Rin because I don't think Kakashi would have told Sasuke that everyone he loved was already dead. He seemed to care about Rin, though probably in a non-romantic way and telling someone that she was dead when she was still alive isn't very nice. In fact, it's quite insulting. =D