Okay, thinking on it more I guess I can make it make sense:
A) The Silence kidnap River, put her in the suit, and it kills the Doctor entirely out of her control. This event, combined with the complicated spacetime objects that are River Song and the Doctor as well as the nature of Lake Silencio being a "still place" (or whatever term they said made it easier to make a fixed point) creates a full bore fixed point in time.
B) The knowledge of this event spreads around time and space since a bunch of people with time travel tech know about it. Since time can be rewritten this changes a lot of things, including the fact that River learns that she is the one that kills the Doctor while being in the spacesuit from her childhood.
C) In this new version of the timeline, using her knowledge of the future, River figures out a way to subvert the suit's control and does not kill the Doctor which causes time to go kablooey because fixed points can't be rewritten.
This all makes sense, except for the fact that the Doctor uses his foreknowledge of the event to have the Tesselecta get shot instead which will have a significant impact on history since the Fields of Trenzelor stuff will still happen as well as the hundreds of other ways the Doctor will save the universe in the future. I dunno.