404 error for specific link on Mac

Ditch the link that you received in the email. Email links are often a vector for distribution of malware links, and the fact that this link doesn't work properly smacks of something not right.

Using your daughter's favorite browser, navigate directly to the website in question and then bookmark it (in Safari it's ⌘D). Optionally, add the web location to the Dock and keep it there as a clickable icon using Safari > File > Add to Dock... command.

Have you tried accessing the link with a different browser? At this point we do not know what macOS version or browser she is using. I'm finding a number of web sites that do not play well with older versions of Safari for Mac. It's possible your iPads work because they have newer versions.

If you do "About the Mac.." on her computer and tell us what macOS version it is running, we can better make recommendations in this setting where we can neither see nor remotely access your computer. Right now, "Apple mac laptop" does give us much to go on, as Apple has made laptops for a very long time.

She might ship an email to the IT folks at the school to alert them to the problem and ask their guidance.

It may or may not be something they are aware of. Also let the instructor(s) know that she is having trouble with the site and she may have options for turning in the work.

You don't say exactly which Mac your daughter has, nor the OS version, but to Empty Caches in Safari for newer Macs running Ventura or newer, you first have to show the Develop menu. It's easy.

If you don't already see Develop in the Safari menu bar, choose Safari > Preferences > Advanced, then check mark the box for “Show features for web developers” at the bottom of the panel.

Then you can simply click Develop > Empty Caches. That's all there is to it.

You’re welcome.