Don't chase a guinea hen off of her nest. What she will do is abandon the nest and find a more hidden spot to lay.
What I did was to collect their eggs after I had herded them in to the coop for the night. I found that leaving at least 3 fake eggs in the nest worked the best for getting them to return to nest the next day.
It is a whole lot better to collect their eggs from a known nest location than to have to keep hunting for their new nests.
To keep them alive, make sure that you have them shut in, in a secure coop for the night. You can do so by training them to go into the coop with treats or training them to be herded into the coop.