This is not at all unusual! Of my six indoor cats, two are coardboard chewers. My impression is that they like the way it feels on their gums. My cats don't swallow the cardboard, but instead simply chew it and try to tear it. So, as far as I know, there is nothing to worry about. (However, do not allow them to chew boxes that might have pesticides on them, such as banana or other fruit shipping boxes.)
Welcome - but be careful, because this site is addictive! It sounds as if you have a cardboard box junkie - a quite common affliction. Our cat doesn't chew the boxes, but he sleeps and plays in them, and rubs himself against them all the time. At first I was afraid that he was "sniffing glue", but then found that he reacted the same way to boxes that were taped, stapled or unsealed, so it must be the cardboard. He gets all excited when he sees the UPS or P.O. delivery truck, since that usually means a new cardboard box! For the past five years, almost, a cardboard box has been a living room fixture. As long as your cat isn't actually eating the cardboard, I wouldn't worry about it. Let her have her fun.
It really is common. Shredder use to do it all the time.If your cat is eating the boxes then take them away from her. Mostly they just shred them. If she is eating them, introduce fiber into her diet to help push it through her system- and hope she run across any staples or tape-