Kaatje Muller-de Vries was married to Joseph Muller. The couple lived at 122 Gedempte Zuiderdiep in Groningen. They had a child who survived the war. The couple had a several items of jewelry looted from them at Westerbork.
The archive of the Stichting Sieraden-Comité contains a list of looted items of jewelry, a statement taken under oath and a statement of the right to inheritance.
NIOD, Records Stichting Sieraden-Comité, box HF 11, file 162
In addition, a Jokos file (number 35862) on this family is at the Amsterdam Municipal Archive. Access is subject to authorization from the Stichting Joods Maatschappelijk Werk.