In hindsight, you tell her not to mess with the system
or that the system will hamper your life at work.
Jokes aside, if your system is logged in(be it as an administrator or a regular user) with it being used as a hotspot generator/AP it's best you add a password on your system(that is required during login) and put the system to
lock screen.
Further reading.
If she knows your password, you will have to change it. This does not however solve the issue since one of your children won't have access to it while it's highly possible that the one using your desktop for shows can be bullied for the new password, rendering your long route useless.
If the system is used as a hotspot generator I'd suggest you leave the desktop as is and invest in a wireless range extender. I apologize if I've misinterpreted your post but that's how I've read it to be.