Can we just remember, River just lost two of the three people she trusts. She never got to say goodbye to her father, and she could only kiss her mothers hand because she had to watch that angel. The Doctor breaks down, he screams and cries while his wife stands composed. From the very beginning to the end of her life, River has silently sacrificed herself for those around her. She may have the feistiness of her mother but she has inherited the great burden of compassion from her father.
Also the fact that she was so surprised to see Rory on Demons Run, because, more than likely this was after Angels Take Manhattan for her