Not to worry. She'll spit it out. It may take a little while, but she will. And I doubt she'll regurge. Snakes get all manner of stuff in their mouths and manage. It's true its not ideal and good for you for using the cardboard, but I really wouldn't worry about this little piece. I've had Ella end up with a mouthful and she was fine. They get pretty creative in spitting out the pieces, lol...