Hillary will appear polished and prepared because she will ALREADY know each and every question in advance and possibly even how Trump will respond.
I hope Team Trump is doing most of their pre-debate discussions IN PERSON and not via email or on the phone. Even 'in person' isn't a sure bet to keep things secret if there is a 'BUG' OR A MOLE on the inside.
She doesn’t need to prepare for the questions. She will wear an earpiece and experts on her team have formulated answers or can come up with good ones on the fly.