I've been an avid user of MS Office long MS bundled those products into one packages and called it MS Office. That said, one of my goals in life - what's left of it anyway - is to avoid paying a recurring annual fee for it. So I don't and hopefully never will use Office 365.
With Office 2016 products, you can easily do a "Repair" through Control Panel > Programs and Features, then highlight the entry for Office, and click on "Change". From there, you get prompted to run a "Repair". With Office 2016, I have the option to run a local repair, or on-line. Either way, the process with check all the Office products and if any problems detected, attempt to repair them - without destroying any user files.
Hopefully with Office 365, there is a similar option.
That said, school districts typically have IT support people on staff. Since that computer is a school asset, IMO, they are the ones who should be fixing this, ESPECIALLY now since your friend can demonstrate "at will" there is a problem with Office 365 on that computer.