Kestrel, our silver and taffy tortie, loves to chew paper and cardboard; always has; no clue why and she's been with us for over 10 years...
Her favorite is cardboard boxes. She likes to bite the paper and tear off chunks, spitting them out; so I give her the flats that the cat cans come in. This seems to keep her focus off of papers we don't want her shredding.
It may be a phase, boredom, some missing nutrient???
Has she been spayed. My cat shredded paper whilst she was preg and used it for her nest, But I am unsure as to why yours is eating it.
x