My cat has been chewing on plastic?

I'm not sure if she has been trying to eat it or not because everytime I catch her, I take it from her. but its everything from grocery bags to cellophane from cigarette boxes. what should I do because I know this could really hurt her. I can stop her inside but not when she goes outside. am I doing something wrong with her and she is depressed? like what should I do? I really dont want her to die or anything cuz I kow its terrible for her.