I'm not sure what's your exact problem is with her Mac or if there really is one, but maybe have a read here in case it can help explain things:However, there’s a weirdie, too. She has two HDs, as pictured.
Add, delete, or erase APFS volumes in Disk Utility on Mac
In Disk Utility on Mac, add, delete, or erase APFS volumes.
I understand that a lot of things changed when Apple's switched to APFS starting with Catalina I believe. That includes how the various volumes are displayed and what is stored in each.
Some of the other Mac forums can probably explain things better for you such as Mac-forums.com.
I'm still happy using Mac OS X 10.9.5 Mavericks and most things are still as they always were.