I am referring to installing the OS, not creating an installer. If could you put her Mac in Internet Recovery Mode by holding Shift+ Option+ Command+ R at startup (this installs the OS that came with the Mac from the Internet which should be Sierra), she could just install the Sierra OS right on the Thumb Drive. I am unsure if it would open on your friend's Mac since she has 10.15. I think the installer, once downloaded, needs to be opened once IIRC.
I think there might be some problems though. Sudo /Applications/Install\ macOS\ Sierra.app/Contents/Resources/createinstallmedia -volume /Volumes/10.12 -applicationpath /Applications/Install\ macOS\ Sierra.app This might be old, but this is what I used for Terminal to create my Sierra Installer:
Can you post the How-To that you are using?Īlso, how are you formatting the Thumb Drive?
