Personally I think it involves agency. We all need the opportunities to choose and the challenges and chances to grow. Heavenly Father knows what choices we will make, He didn't send us here to fail. Those who become sons of perdition become that because of choices that they made, not because of Heavenly Father. We each have agency, we chose to come to earth. We chose to accept the Plan of Salvation, Heavenly Father's plan and not Satan's plan in the counsel of Heaven, which is ultimately the plan that your student is talking about. I think the counsel in Alma 13 talks about men being called from the foundation of the world and then because they chose to be faithful, they received the calling in this life.
It is essential that she realizes that this life is a test for ourselves as much as for Heavenly Father. We are here to learn that we can live away from Him and make correct choices. It is to prove to ourselves and to Him that we have testimonies, that we can be obedient and follow His plan to return to Him. Predestination is not church doctrine. Here is an
Ensign Article that might help to explain the difference to her.
Good luck. This is the kind of question that I threw at my teachers when I was struggling and wanting to stump them up. I hope that the article helps some. Basically it comes down to accepting the Plan of Salvation.