The confirmation came from the Steam support staff earlier this month when Resetera forum user delete12345 asked Steam support if he can put his Steam library in...
Same but under mine, we are starting to split who buys a bit more now since our kids want to play different games at the same time. Time to start spreading them across 4 accounts soon
IIRC, they are in beta testing to allow multiple people play multiple games from same account at same time, and you can now buy multiple licenses for your account so can both play same game at same time on same account . Don't ask me the specifics, I only know that I can buy multiple licenses for my account currently.
You can access her Steam anyway through account sharing. If she has a unique Steam password I don't see the difference.
My wife and I know how to access each other's e-mail. We've never done it, but if anything happens to me she can access and pay the bills that come in. If nothing else I'd recommend something in your will or an "open if I die" envelope with your passwords in it.