She was the vice-chairwoman of the VVD party in the House of Representatives from 2003–2006. In 2006, the chair of the VVD party in the House of Representatives, Jozias van Aartsen, stepped down because of the poor VVD election results in the 2006 Dutch municipal election. De Vries followed van Aartsen's example because she felt "connected" to him. Fellow VVD Parliament member Edith Schippers succeeded her as vice-chairwoman.
In the House of Representatives, she was associated for her party with economical and financial affairs like pensions, unemployment, and the like. She was chairwoman of the House of Representatives Commission for Government Expenses and was part of the Srebrenica Commission, which investigated the errors made by the Dutch UN army unit regarding the Srebrenica massacre in the BosnianSrebrenicaenclave.