Louise was born as the daughter of Prince William of Hesse-Kassel and Princess Charlotte of Denmark. Her siblings included Princess Marie Luise Charlotte of Hesse-Kassel, Prince Frederick William of Hesse-Kassel and Princess Auguste Sophie Friederike of Hesse-Kassel. Louise of Hesse lived in Denmark from the age of three.
Princess Sophie Johanna Maria of Isenberg was born on 7 March 1978 in Frankfurt, West Germany, to Franz-Alexander, Prince of Isenburg (born 1943), and his wife, Countess Christine von Saurma zu der Jeltsch (born 1941). Her father is head of a mediatized Catholic line of Princes of the Holy Roman Empire, who lost their independence in 1815.