My opinion is that she set it up, it didn't work at first, she didn't use it, forgot that it existed, and here we are.
> Apple devices share fingerprint matching details and another device had her details
I looked into it quite seriously for windows thinkpads, unless Apple do it differently, you cannot share fingerprint, they're in a local chip and never move.
So how does TouchID on an external keyboard work without having to re-set up fingerprints?
Presumably the fingerprint data is stored in the Mac's Secure Enclave, and the external keyboard is just a reader