Could you try poking holes in balsa wood (which should be easy to do with a screw driver or similar), and stick some paper towel through the holes?? This might encourage Birdie to chew on the balsa while she’s ripping up the paper towel. Another favourite shredding material is Sola wood sticks, very similar to balsa but a bit lighter. You can buy these from most good sites that sell bird toy parts and again, cut them to size, pine holes through them and thread some paper towel. Raffia is another option (especially for threading through the holes in the balsa or sola wood).