Born to Prince Eduard of Saxe-Altenburg and Princess Amalie of Hohenzollern-Sigmaringen, Thérèse spent her childhood in Bavaria.

After her father's death in 1852, she lived with her cousin, Queen Marie of Hanover, and later with her maternal uncle, Karl Anton, Prince of Hohenzollern.

In 1864, Prince August of Sweden and Norway, Duke of Dalarna visited her in Düsseldorf, and after he had spent a week to get to know her, their engagement was announced.

During that time, she upheld a correspondence with Ohan Demirgian, a known Armenian con-artist with whom she made an acquaintance in 1869, when his presence at court caused a scandal.

In 1875, Fritz von Dardel wrote: "The Duchess of Dalarna is now declared to be out of her senses by her relatives in Germany and at their request, she will remain in Switzerland over the winter to be treated by a doctor."