Alfie loves boxes and will spend hours shredding them. He pays absolutely no attention to me if he has a good box to shred.
Some people advise against giving boxes in case it promotes nesting behaviours but thankfully I've never had this issue with Alfie.
You can mix it up as well, add some shredded paper or foot toys or trees to the box so she finds them as she shreds the box. Or like timersmom says, a box within a box within a box. The best box Alfie had was from a friend who had ordered some beers for his brother online. He donated the box they came in for Alfie to shred and it had cardboard partitions in to stop the beer bottles from clashing together during transit. Alfie thought all his Christmases and birthdays had come at once with that one. Decent crunchy cardboard with 12 small sections to get through- it kept him going for weeks! 🤣