I did the same as Joy and reviewed "The End of Time, pt 2" with special focus on "The Woman". One thing in particular stuck out for me. When The Doctor is confronting Rassilon, and trying to discern what to do... he looks right at this woman. She gives him a furtive glance with her eyes toward the Master's machine. During that exchange between her and the Docotr, you can hear the gentle strains of what I've come to call "Donna's Theme". It's a very wistful, sad bit played in a minor key with a little bit of vocalizing. The only time I have ever heard that piece played is when Donna is in a scene or the focus is clearly upon her. "Turn Left" is a perfect example. That to me indicates there is some strange connection between "the Woman" and Donna. Is that enough to say she's Donna in a diffrent timeframe? That she's potentially the Doctor's mother? No, it isn't, or else this discussion would be over. But I am convinced that she is in some deep, veiled way connected to Donna.