Hi Suzanne,
Thanks for posting your question. First, may I ask if your site’s member made any reference to assistive technology such as a screen reader or speech recognition software when submitting their support request? I have performed a quick task-based test on the page in question using NVDA (a screen reader) and Firefox, (latest version), and I am indeed unable to activate the + symbol using a keyboard. Assistive technologies such as screen readers are operated by keyboard and not mouse, since a blind person is unable to see the screen for themselves and so cannot accurately move a cursor with a mouse.
If the member in question has indicated that they’re using assistive technology of some kind, (screen readers include NVDA, Jaws for Windows, Window Eyes, Supernova and VoiceOver on PC/Mack and VoiceOver or Talkback on iOS and Android devices respectively), there is unfortunately no way for that member to interact with this table, (or any other table created by this plugin and its extensions), in anything other than a very basic manner.
Before I go any further with proposing a possible solution, I’ll wait for your response, because that will determine how to proceed.
Amanda