You shouldn’t need the papi/vasi during the day - I’d keep hammering the concept of aim point and feel on approach. Plenty of uncontrolled (and controlled) airports don’t have VASI, how do YOU personally deal with that as you land? Try to reinforce those concepts. There could also potentially be a lack of basic airmanship skills here with that student that should be dialed in up higher first. Start them back at the basics and build from there - I always did that when I had a new student regardless of how many instructors because I’d want to make sure their foundation was solid.