Can I switch between two users in a single click?

Not a single click, but I can give you a keyboard shortcut solution.

Go into the menu to set custom keyboard shortcuts

and add a new one with this command:

dm-tool switch-to-user suzi

Assuming suzi is your wife's username, and set a shortcut of your choice by clicking where is says "disabled" and then pressing the key combination you want to use (for example, super+alt+S if the user's initial is S). Set another shortcut to switch to your own account (with your own username in the command).

You can us a Function Key combination. F1 is the first DISPLAY, then F2, F3, etc.

If you were the first one logged in your DISPLAY would be F1. The next user's DISPLAY would be F2.

So you can quickly swwitch between user's by hitting Alt+Ctrl+F#

With this method you can save having to login when switching between sessions.