I haven't seen any dual-voltage rice cookers but if they exist they'll probably be more expensive than single voltage rice cookers for overseas markets. I bought a small Toshiba rice cooker in Tokyo some years ago and while it seemed almost impossible to buy a simple rice cooker made for the Japanese market it was possible to buy a simple 220-240v cooker at a reasonable price.

It should be possible to use a Japanese 100V rice cooker with a suitable transformer but the cost of such a transformer might exceed the price difference unless your wife insists on buying a fancy Japanese rice cooker or she already has a cooker she would like to bring over to Europe.

Your wife may like to check the following websites

http://komachi.yomiuri.co.jp/t/2012/0809/530651.htm
http://q.hatena.ne.jp/1156869221

or search the internet for 炊飯器 変圧器 容量