Jailbreak question for '21 Paperwhite

Hiya- I would like to give a friend a '21 Paperwhite, and set her up to sideload books via Calibre. It would also be great to be able to email .mobi files to the device. I have a few questions.

1. Can I prevent automatic updates? I don't want her to get an update which prevents sideloading.

2. Should I just tell her to turn off wi-fi indefinitely and sideload everthing?

Any advice much appreciated. thanks!