It had nothing to do with Ripley. In the extended version, you see newt's parents find the same spaceship that the crew of the Nostromo found. They also found the Alien eggs, which open upon proximity to a living being. One of Newt's parents gets facehugged and that's that.
Ripley being found just in time for this is either fate, or pretty much the only way to give people a movie they'd want to watch
