[1][better source needed] After the death of her husband in 1638, she acted as regent on behalf of his son Philip Louis III.

The accession of Frederick Casimir took place during the Thirty Years' War, which left him in a financially awkward situation.

This union with the Dowager Countess had the effect of calming Frederick Casimir's Reformist subjects in Hanau-Münzenberg who looked upon the new Lutheran Count with suspicion.

The marriage remained childless probably due to the great difference in age between the spouses: Sybille Christine was 20 years older than Frederick Casimir.

The union was characterized by other differences as well, partly because Frederick Casimir relied on his wife's property to subsidize his spending habits.