Not only that: Since the game is a different port of the game altogether she would have to buy the newer version of the game on PS5 again. If she can and had the game bought only for playing with you, try to refund the game.
The PS4 game was made from an early version of 7D2D on PC and ported by a company that folded some years ago. It never will get any updates and it can never be compatible with the current 7D2D, the hardware of the PS4 is just too weak for that.