A única maneira de responder isso é com, como River ou o Doctor diria, "spoilers".
River Song is the result of an attempt to create a weapon that could be used against the Doctor to kill him. She is Amy Pond's daughter, taken from her at birth. The next time, in River's timeline, as of now, that she sees Amy is when she appears as Amy's friend Melody.
It is a rather convoluted timeline, which would probably be much easier to follow if River's timeline (in terms of meeting the Doctor) weren't running backwards.
