During World War II, she was active as a Swedish spy as an employée of August Fincke, the German attaché of trade in Stockholm.
Wendt was of partially Jewish ancestry, and her father's publication business in Stralsund had been confiscated by the Nazis.
She provided information about secret Gestapo operations and agents active in Sweden under the code name Onkel (Uncle).
After this, Wendt received an order to return to Germany, not knowing that she was to be executed, and was taken into custody by the Swedish security police which provided her with a new identity.
She lived the rest of her life in Sweden and published her memoirs in 1993.