All settings missing under "Find My" except "Find My iPhone"

Hi,

My mother in law is experiencing a strange issue on her new iPhone. She recently migrated to a new iPhone (7 to SE). The old iPhone has been removed from Find My. However she is unable now to share her location with anyone (mainly my wife :-)). When taking a look in Settings - Apple Account - Find My, then only the menu item "Find My iPhone" is present. The rest of the settings page remains blank, meaning there is no "My Location" and no "Share My Location", like on our iPhones. When switching into the "Find My" app, the location services are on, they're set to "While using the app" in settings, and that they are active is also indicated by the arrow next to the clock when running "Find My". When clicking on "Me" in the "Find My" app, all options like "Share My Location" are simply not there as well. The whole menu under "Me" starts at the "Notifications" menu entry.

iMessage works fine, meaning my mother in law can send us "blue bubbles". She can also send "Check In" attachments in iMessage without any errors popping up but, it doesn't seem to have any effect on the recipient's iPhone, meaning we don't see her location.

What we have tried so far:

We already updated the iPhone to the most recent iOS version, didn't change anything regarding the behaviour.

We completely signed out of iCloud and signed in again - no change and of course rebooted in between.

It's looks like the old iPhone, which doesn't show up anywhere in iCloud, also when using Safari to logon to www.icloud.com, would still be in charge of determining the location.

To be fair, she had some bloke in a mobile-phone shop do the migration from the old iPhone to the new one. So I cannot fathom what he could have done wrong to screw up a simple transfer like this.

Any ideas would be greatly appreciated!

Regards