Why no sound in zoom?

I am trying to remotely help a (not techie) lady fix a problem with Zoom. She is on a Windows 10 desktop. She does not have a webcam or microphone - but that's not a problem because she just want to watch and listen.

She has used Zoom before without problem, but last week she joined a zoom meeting and was able to see the video, but unable to get any sound. Sound on the machine is working - she can watch youtube videos etc with sound - no problem.

I set up a zoom meeting and she joined using Edge, and video worked, but again no sound. There is an option in Zoom to test audio - she tried this and sound came out of her speakers just fine. However she was unable to hear anything I said via Zoom.

Sound settings in Windows all look fine.

What else should I be looking at?

Thanks,
Roy