Find My not showing contact location but phone device does

I’ve read a bunch of people on here with similar issues.

My daughters phone has stopped sending her location until she gets to WiFi or plugs in possibly.

Curiously, as others have noticed, her personal iPhone which is configured to send her location manages to track under devices just fine. So it’s really odd that it doesn’t send her contact location at the same time.

I’ve just found out she’s running it in power saver mode most of the time which might indicate why it pings home less, but it seems to consistently be the last known location before she left.

My theory is that;

a) power saver doesn’t ping the contacts location unless plugged in or it connects to WiFi (saving cell power).

b) the device is still live tracking as long as she’s walking with another iPhone user because the device finder works through the Apple network like AirTags do, and doesn’t need the phone’s cell transmitter.

Only a theory, but I’d be grateful if somebody from Apple could confirm this quirk of operating and why it works this way.

Seems busted.