@nutter: I get what you're saying, but honestly I don't think we're there quite yet.
There are also issues beyond trust, more relating to convenience. I don't want to have to sign in and out of all my accounts (Steam, Twitter, Google, etc.) every time I use my PC. Also we both use Windows under different languages and different keyboard layouts. We also don't want Windows to copy our photographs in the same folders, because we have different ways of managing that stuff.
@nyxtowa: I forgot that Steam family sharing is a thing. It's been so great to be able to share all my games with her on the consoles, especially since she can access a large Game Pass library on the Xbox through my subscription. We will definitely give this a try once I get the account and hard-drive stuff sorted.