Make sure the nest is open and ready when she starts to lay. I recommend 16 weeks, although it will likely be several weeks after that when they start.
Put a fake egg in the nest. A golf ball, a wooden or rock egg, a plastic Easter egg (half filled with sand and glued shut) work well.
Make sure the lip on your nest is high enough that they cannot scratch out the fake or real eggs or the nesting material.
I made my nest boxes so I could lock a hen in there if I wanted to. When I have one that is laying where I do not want her to lay, I catch her when she is laying the egg in the bad nest and lock her in the nest until she lays, then let her go. Usually it only takes a half hour but I had a stubborn Speckled Sussex that took several hours and two different days. She did learn eventually.