Nice choice in camera, I hope she likes it.
On the focus question, I believe she's in an auto focus mode and perhaps in continuous focus. To change the focus mode on mine which is a Z6ii I'd push the "i" button on the camera back to pull up a menu grid. On the bottom right of the menu grid is a square that will have either "AF-S, AF-C OR MF" for single, continuous or manual. Right above it on the grid are the options for focus mode which are icons representing pinpoint, single point, dynamic area etc. There are a few different ways of changing the setting but for now I'd use the "i" button and select AF-S and single point. That will stop the focus from "jumping around". She's going to have a lot more questions than that though so I'd suggest downloading a copy of the user manual and reference manual from the Nikon web site and also reading the following article on the Photography Life web site for tutorials:

https://photographylife.com/category/photography-tutorials
Z5 settings: https://photographylife.com/category/photography-tutorials
beginner's guide: https://photographylife.com/category/photography-tutorials

Could this be her first 2021 resolution?

My wife's daughter received a nice Z5 with the 24-200 lens for Christmas. Her camera prior to the Z5 was an iPhone 10 (?) and long abandoned Rebel. She's starting out in "Intelligent Auto" mode and is frustrating by the bouncing focus point. I did a quick look at the menu system and browsed the manual but kind of came up empty. Is fixed single AF point available in the Z5 Auto mode and if so, how is it set from the bouncing squares? Also, when you change camera operating modes, do you have to customize some menu settings for each mode? For AP and SP, I was able to make the change but when she selected Auto on the mode dial, the camera seems (?) to revert to the auto focus seeking boxes? I suggested she jump right to AP, but she's determined to go the Auto route in "Auto" for now. Help from you Nikon folks would be appreciated. Thx and Happy New Year.