Guess it depends where she will be. In general though, ATM's are becoming commonplace. So for daily expenses with decent fee and exchange rate schedules, the atm card is handy. A visa ATM might prove doubly useful.
Visa is probably most commonly accepted but your own card company (read especially chase and citibank - my experience and that of others I've spoken with) may deny transactions in many places, even if you have informed them of your travel prior to leaving. Both companies caused my wife no end of misery on one business trip to eastern europe. She called me wondering why her transactions were being denied. I contacted the card issuers and customer service people assured me the transactions would be approved. Of course, nothing of the sort happend despite their assurances. Atm pulled her through as no visa transactions were autherized by said companies. When I COMPLAINED, they told me they were just trying to protect me. Yeah!
I've heard of the same happening to others in parts of Europe and Asia.
Amex has great personal service overseas but it's important to set them up prior to leaving. And of course, fewer places accept Amex, especially if you're traveling Rick Steve's style.
Have her make photocopies of her cards and keep those copies in a safe place - just in case they are lost or stolen. Makes cleaning up that whole mess easier now that Karl Malden is gone.