You will get better functionality from autocomplete if you she uses her own account. If you share some logins and you want to make duplication management easier then you will want an organization.
So 3, once you have an organization you will transfer the entries through the share function. You will find more information in the help files.
Option number 3 works for our family. We both have two Premium individual accounts ($20.00 per year) because we are using Yubikeys for 2FA login authentication. See here for the basic setup procedure:
Note this is a page of the Bitwarden manual and you can find much more information about Sharing by looking for that topic in the left pane of this page. (If I remember correctly, I could just check-mark all of the links that I wanted to share and share all of them with one click.)
I understand that it will work. Remember that there is a Free Two Person Organization plan available and you are just using a modified version of that plan where you have upgrade one of the two user accounts to Premium. Be aware that your wife will not have the premium Individual Plan features available on her vault.
My worry was that I would lose the Premium features of the Individual account when I joined the Free Two Person Organization. I did not.
Actually, I think a diagram of an Free Organization setup as being three circles with each circle being a separate vault. One circle for each individual vault and the third circle representing the Organization vault. There is a connecting link between each individual vault and the organization vault. All of the shared items are moved into the Organizational vault.