After a beat, Riven laughed gently. "Oh, Donna," she said, eyes twinkling. "I very much like you. Think about it for a moment. How often did the Doctor speak to you about his previous companions? Who they were, what happened to them? Over all his life, all his regenerations? Everything dies. Everyone, eventually. Sooner or later. Any nobody knows it like the Doctor." She put a hand on Donna's arm, her smile warming. "But I think all the suns in all the worlds would go dark if he ever, for even a moment, accepted it."
She slid her hands casually into her pockets looking back at the city around them. "You were good for him, too. More than you know. In a way, for just a while, you were the most important woman in all the universe. Just because of who you are. Just by being you." Her eyes shifted, returning to look at Donna. "You don't want to spoil that for yourself, now, do you?"
As far as what was going on with New York, River nodded and absorbed the information. No answers, not yet, but the differences were cataloging themselves in her mind. "Anyone notable?" she asked. Knocking on doors to find the excitement was bloody boring, but knowing there was a mystery around had sharpened her interest considerably.