Screen Sharing does not generate Share Screen notification on Macbook Air

I've used screen sharing to help provide support for remote family members for years. I haven't run it in some time and in trying to provide help today, I found I could not make it work on my mom's remote MacBook Air. Specifically, she never gets a pop-up alert asking to share her screen.

I verified today that screen sharing still works allowing my iMac to control the screen on a new MBA running Sequoia 15.6.1 and an Intel-vintage MBA running Ventura 13.7.6. Both work without issue. However when I try to send my mom a request to share her screen (same Intel-vintage MBA though this one is at Sequoia 15.7.1), it never prompts her with the notification so she can accept or reject the request. Her system does "ding" with a notification alert shortly after I send her each connection request but the text alert box never appears on her screen, so she cannot accept (or reject) the request. It's as if it has received the alert but the system cannot display it for some reason. So it dings on her end, nothing is shown on the screen, and maybe 30 secs later it times out on my end, stating that she is not available.

I've double-checked a number of things:

• Screen sharing is enabled--I set it to allow all users.
• Notifications are enabled overall.
• Screen Sharing app notifications are allowed and set to alert. All options lock screen, notification center, etc are enabled.
• Messaging app allows us to communicate without issue.
• The system has been rebooted and is current.
• I've shut down all other apps on her end.
• I generated the share screen request from Messages and from Screen Sharing app with the same results.
• I have pointed this request to both her phone number and her apple id--both yield the same results.

Any thoughts on what I'm missing?