Her mother died in 1589, and she was placed in the care of the German Euphrosina Heldina von Dieffenau, whom she praised much later in life.

She reportedly got along well with her stepmother and was close to her half siblings, especially her eldest brother, the future King Gustavus Adolphus, who is noted to have been very affectionate toward her.

Although she was a great heiress, her status on the international royal marriage market was uncertain because of the political situation in Sweden after her father had conquered the throne from his nephew Sigismund.

The death of her younger brother in Sweden, as well as the lack of heirs to the Swedish throne was evidently the reason why the monarch wished to move her to safety away from the Thirty Years' War.

Catherine and John Casimir settled in well at Stegeborg, where they maintained a royal standard of living: they kept a court with sixty formal ladies-in-waiting and courtiers and an official table.

Catherine was exposed to certain intrigues at court with the purpose of blackening her name in the eyes of the royal couple, but she managed to avoid these plots.

In 1631, Catherine was given the custody of her niece, Princess Christina, the heir to the throne, when the queen was allowed to join the king in Germany, where he participated in the Thirty Years' War.

After the death of King Gustavus Adolphus, the couple came in conflict with the Guardian Government of Queen Christina over their position and rights to Stegeborg.

[2] One example was at the opening of Parliament in 1633, when Catherine in accordance with the wish of the Royal Council followed Queen Christina in the procession, while John Casimir was given the choice to stand and watch the ceremony from a window or not be present at all.

[3] After her death, the royal council appointed two foster mothers for the queen to replace her: countess Ebba Leijonhufvud and Christina Natt och Dag.

Catherine was frequently pregnant, giving birth to eight children in fifteen years, but only five of them survived childhood: All kings of Sweden following her son, except three (Frederick I, Charles XIV John and Oscar I), have descended from her.