Solutions for slow playback in review on Macbook Pro 2016?

Hi all. I have a problem that's a bit mystifying. I have a coworker with whom I share courses for review. When she plays back the content, the next buttons take too long to respond, as do the close buttons for layers. "Submit" buttons on quizzes also take too long to respond. In general, things are just .... laggy (how's that for a technical term?). 

It's odd. She has 16gb of RAM, still a ton of available disk space, and her internet speed is up to snuff (we have zoom meetings all the time when no issues). I believe she's running the course in Chrome.  I should add that the courses run with no issues on my 2017 iMac with similar specs (though it's obviously a year newer with a better graphics card). 

Have any of you encountered something like this? Is there something obvious I should suggest to her? Thanks for your help.