It is indeed a browser setting to open new windows in a tab or not. But I’ve found that you can usually override the browser setting and force it to open in an actual popup window by checking some of the New Window Properties like “No Menubar”, “No Toolbar”, “No Status Bar”, and “No Location bar”. I usually check all 4 of those, but you may need to experiment to see what works best in her particular situation.
Instead of using the Display Page in Pop Up action, use the Go To action and indicate you want the page displayed in a new window. This will give you the ability to edit the window properties as mentioned above. See screenshot attached.