If she is tearing up the boxes I wouldn't worry, if she is actually eating the pieces, I would advise you to take her to the vet for bloodwork. She could have something in her diet lacking that is causing her to eat strange things.One simple blood test will confirm it and a change in her eating program will cure it. If she is just tearing up the boxes, she is just having fun!
I leave out paper bags, they roll there bell balls in them and kill it, then have fun tearing up the bags over a couple of day period. Picking up all the little pieces of bag sucks, but a labor of love..
My cat Lucky sits like this - it's so funny. He doesn't do it much now as he has arthritis in his spine but sometimes in the middle of grooming he'll just stop and sit like this, perfectly comfortable making us laugh. He doesn't demolish boxes like your baby though !