Immediately becoming an armed freedom fighter, she initially operated in the Netherlands province of North Brabant, gathering intelligence, delivering medication to Allied and Resistance troops in the north and performing courier duties for her resistance cell while also helping to free captive Dutch citizens from the prison at Mariënhof, the Herzogenbusch concentration camp in Vught, and Kamp Sint-Michielsgestel.

Hiding soldiers, businessmen and political figures in the attic of a secret annex he had built into the van Grunsven home, which was located in one of Geffen's more secluded areas, he then hid more at-risk individuals in a shelter he had constructed outside between two wooded hills.

Dressed in a nurse's uniform and carrying a 6.35 mm revolver, she infiltrated the prison at Mariënhof by bribing a guard with a bottle of wine laced with sleeping medication.

Operating with her colleagues via the waterways of the Biesbosch and the Merwede, she risked her life numerous times to make this line crossing as a courier, transferring vital information to Allied troops under the aliases of “Ice Block” and “Trouble.” While engaged in one of these missions during the winter of 1944–1945, she was permanently partially paralyzed during a fall in which she damaged a cervical vertebra.

[10] After her nation was liberated from its German occupiers in May 1945, word of her dangerous exploits spread via newspaper reports, which heralded her valor while also documenting her injury and partial paralysis.

The State Secretaries of War and Navy, the Commissioner of the Kings in South Holland, General H. J.Kruls and many other military and civil authorities attended the ceremony on a site at the Merwesingel....

), who successfully performed dangerous assignments in occupied Holland sixteen times in the winter of 1944–1945 before injuring a cervical vertebra on the ice while on a mission in bad weather.

The Prince handed out the awards to her, while she lay on a stretcher, and sat with her for a few moments.She also began her own family, becoming Riet van de Haterd-van Grunsven, the religious marriage ceremony was being led by the priest she had rescued in 1944.