Probably enabled it at some point and forgot. Perhaps even during setup when the computer was new.

My recollection is the computers do by default ask the user to set up biometrics

I want to say that is generous of her, but one thing that is weird is if I didn’t want someone to go into my laptop and they tried to force me to use my fingerprint to unlock it, I definitely wouldn’t use the finger I use to unlock it on the first try. Hopefully, Apple locks it out and forces a password if you use the wrong finger “accidentally” a couple of times.