No they don't. They encrypt them in the background after explicitly telling you and flashing up a dialogue box which you can't avoid which gives you the option to sync your key (or not), or print the key, or save the key to the USB stick. Literally 1 of 3, you can't not select an option, and it's a full screen dialogue so you can't provision your computer without acknowledging that the encryption is happening.
Additionally if the OP's case were a new computer than they wouldn't have gotten that far since apparently the sister doesn't even know the password to her account (which is strictly required to provision a new PC)
Learn to recognise when you're being bullshitted to.
so if a user forgot which e-mail address they happened to give during setup, or no longer have access to that account
Yes, users forgetting things is dumb, including users not writing down bitlocker recover keys, or printing them out. Maybe, just maybe, losing everything due to their stupidity can teach them a lesson.
Apparently, it's not ransomware when Microsoft does it.
Tell me you don't know what ransomware is without telling us.