Regular people have been carrying house keys and/or car keys around for practically their entire lives. A physical key for their computers wouldn't be weird, except it's different than what they're used to.
The concept that if I lose my key I am totally screwed doesn’t align.
So in the end she was locked out of the encrypted backups and had to wipe the phone, losing photos and a lot of notes. Despite all this, somehow expected that a quick ring to the <Cell Provider> call center could get her files unlocked and restored. Once that proved fruitless, that a call to Google would do the trick.
Notary public... the new digital locksmith for password recovery.