Yes, she needs to use your email and password to access your system on the Sonos app.

No, she can use the app without logging into an account, unless she wants to change its configuration which will require authentication to your Sonos account.

Thanks for the response.  Can you explain what “authentication to your Sonos account” means?

I don’t know if you and your wife share passwords and in this case it does not matter. If you have the password for the SONOS account, you can install the App on her phone in private, then hand the phone over to her. This is a one time setup unless the App is reinstalled in the future.

Thank you.  And does this approach enable my wife to play her own music or is it a shared account (we have different tastes!)

You can install multiple (for instance) Spotify accounts on the system and have her Sonos app choose her Spotify account.