Folk costumes - Volkstrachten - are traditional clothing that can be highly specific to a region or even a village. The woman in your photo is wearing parts of the Oesterten-Tracht or Lindhorster_Tracht, which was characteristic of eastern Schaumburg-Lippe.
It consists of a characteristic red skirt with colored ribbon trim ("Want"), apron, sleeveless vest with applied lace, ruff (Hällschen), embroidered shawls, and knitted forearm guards ("Handschen") as well as the headgear and headscarves.
Once commonly worn, there are efforts underway to help preserve this and other regional costumes (Tracht des Jahres 2010).