So …. what to do?
We found a work-around, and I think it’s good enough to share. (I’ll be sure to report back later to let you know if this actually works for her over time.)
The fix she tried is this:
Settings > Do Not Disturb > Allow Calls From > All Contacts
So, basically, she is using the Do Not Disturb function 24/7 on her iPhone, and this setting will only allow calls from numbers that are currently in her contacts list.