From 1990 to 1996, Herfkens represented the Netherlands and a number of other countries at the Board of Executive Directors of the World Bank Group in Washington, D.C.

One of her lasting accomplishments was the focusing of Dutch assistance to poorer developing countries that have made real commitments to poverty reduction programs and policies.

She widened the influence of Dutch assistance policies by helping establish in 1999 the Utstein Group consisting of the Ministers for Development Cooperation of Germany, the United Kingdom, Norway and the Netherlands.

In this capacity, Herfkens helped promote the achievement of the Millennium Development Goals through advocacy activities at the global level and in particular in Europe.

In early 2008, the provision by the Dutch government to Herfkens for the use of an apartment – while she was working for the Millennium Campaign and living in New York City during the period November 2002 until January 2006 – stirred up controversy (e.g.[6][7]).

The Minister added in his letter: "I regret that in the public debate the impression was wrongly created that Herfkens acted reproachably vis-a-vis the Ministry by accepting allowances.

The review also concluded that, while Herfkens did break U.N. rules by accepting the use of an apartment whose rent was paid by the Dutch government, she did so unknowingly and in good faith; and that lack of induction, given the haste in which the MDG Campaign office was set up, also contributed to her not being aware of the prohibition of receiving benefits from a Member.