It will help to get her spayed if you haven't already. It will increase her life and make her a lot more comfortable in the years ahead of her. Some cats just really like to shred paper. If your cat is eating the whole thing- paper or cardboard it could be pica and she could have a nutrient lacking in her diet. A vet visit is a good idea IF she is eating and not just shredding the stuff.
One of my cats likes shredding boxes too. Its her favorite thing to do. She also started it after having her kitten. She doesn't eat the boxes though, just makes a big mess for me to clean. I have managed to teach her to only chew boxes I give her so she isn't chewing things I need.