Visa or mastercard is accepted widely in Europe now, while Europeans more often use debit cards. But I do not know how far Euro and American debit card systems are compatible meanwhile? If there is a "Maestro" logo it should work easily. Still there can be fees for getting cash at ATMs. It is uncommon to pay with cards in simple restaurants here, except maybe in Scandinavia.

Traveller's cheques have become totally obsolete, I doubt she could cash them easily. CC is great for travelling.