So nice to hear things keep going well, despite the occasional bump in the road. I quite enjoyed Chicago too (of course I was watching the scenery very carefully )
I have had experience (and success) in my work, treating people with moderate to severe anxiety disorders, using a behavioural approach (with no meds). I have found first of all, that if the person can learn about the condition, this lessens the anxiety already. Anxiety feeds off itself, and if the person fears that they will lose control in public, or even die (which often happens in more severe cases), this in itself can provoke an attack. To be reassured that you will be fine, and most likely you are the only person to notice the signs, can bring about some relief. There is an excellent resource called the anxiety and phobia workbook (can't remember the author offhand) which your W may find helpful.
I don't know if this will be of help to you and your W, but I have helped people by having them identify the sources of their anxiety, and list these. Your W's may be more generalized anxiety, but examples from people I have worked with were often specific situations such as crowds, loud noises, heights, etc. Then I lead them through relaxation exercises, followed by systematic desensitization to the anxiety provoking stimuli, initially just imagined, then very gradually, for real.
It works, but it can take a long time. Of course the people I have worked with have been experiencing debilitating anxiety for a long time, to the point where it limits their activities outside of home.
If your wife can identify what triggers these feelings in her, and find a way to relax in the face of them, her anxiety won't likely evolve to this point. Maybe she could benefit from yoga too??? Or meditation, or even just progressive deep muscle relaxation (you can buy tapes to guide this). I have tried to describe a very detailed process in a paragraph or two here, but if I can be of any more help, please don't hesitate to let me know.
I know she must have been tremendously comforted by you staying with her and helping her through this recent attack - it can be very scary. I have had some mini-attacks myself, mine are actually triggered by a minor heart condition which causes my heart to race suddenly, but with my background knowledge, I was able to sit back and say "isn't this interesting?" instead of being convinced I was having a heart attack. Your ongoing support will be so valuable to her as she learns to cope with this, and overcome it.