Hmm hard to say.
Here, I can use a Visa/Mastercard anywhere. Usually get good exchange rates from the ATM, and have no problems with use. Plus if its stolen, I'm not labile for charges. AMEX is a bit tougher as many places don't take it like at home. I would imagine one of those re loadable prepaid visas would work fine also, if you can with drawl from an ATM. Cash these days is a hassle to carry around and have and with the card, if she charges everything, she won't really have left over currency that she can't use in other countries.
Of course if you would prefer cash, thats always an option. Best method. Get a debit card to a checking account. They are usually Visa/Mastercard, and usually offer protection against theft, and also you can easily add money to the account. Plus, some banks offer free international withdrawls.
One big negative is banks will charge a convience fee usually somewhere around 2% for the card use and if withdrawing from an ATM a $2 transaction fee. But still I find this easier and safer than cash.