Élisabeth-Athénaïs de Saint-Cyr was born in 1750, the eldest daughter of the impoverished Marquis de Montausier. Élisabeth was the eldest of three children, her siblings being Marie-Antoine de Saint-Cyr (later Duchesse de Rochefort), and a younger brother Charles-Sébastien de Saint-Cyr (future Duc de Montausier).
Growing up, Élisabeth, with her darker hair and lighter eyes than most in her family, was described as one of the most beautiful women. Along with her sister Marie-Antoine, they were educated by a governess, who trained the girls in the art of dancing, speaking, writing, literature, music and art. As her mother’s favorite child, Élisabeth was given the best gowns and jewels the impoverished family could afford, leaving her sister without. Spending a lot of time with her mother, Élisabeth resents the governess, who cares greatly for Marie-Antoine and little for the others. Élisabeth grew to be a bold; an intelligent woman with a fierce pride of her mother, and her sister.
In 1765, the Marquise de Montausier took her daughters to Versailles, to introduce them to court. Élisabeth resisted the court etiquette, something she would try to avoid for a long time, and acted shy towards everyone, unlike her sister, who blossomed into a social figure, social enough to catch the eyes of the Duc de Rochefort. Soon her sister was married to him. Being married to the richest man in France, all attention fell to Marie-Antoine de Rohan, Duchesse de Rochefort. Their mother changed her ways, giving all her attention to Marie-Antoine now, causing Élisabeth for some time to hate her sister.
Élisabeth, despite her beauty, charm and grace, was found to be cold by court, and decided to return to the family's Chateau outside of Versailles, where she lived until 1769. In 1769, her father managed to find groom for his daughter, Giovanni Andrea Colonna, the Prince di Paliano. Élisabeth, known as Princess Isabella di Paliano, lived with her new husband at the Prince’s castle in Paliano, where he served the Papal state as an ambassador to Savoy. Despite him being ten years old the couple enjoyed a happy marriage. She her taste of art, society and living lavishly matched his own, although Isabella always yearned to return to France and to Versailles.
In 1770 the Prince left the Papal state, and the couple moved to Melioria, a city known for its social life. It was here, that Élisabeth received the worst news; she found her father had died in france, but couldn’t return, as her own husband had taken ill. Barely a month after her father’s death, the Prince dies. Left in charge of his estates, she closes them and sells it, settling in a small house in Melioria where she remained popular.
By 1771, at the age of 21, on the invitation of her sister the Duchesse de Rochefort, Élisabeth returned to France, and to Versailles, where she gained access to a small apartment. She would always remember her years in Italy as a good time of her life, her manners better trained, with a softer heart, she retunred back at Versailles she became known as Élisabeth-Athénaïs de Colonna, Princesse de Paliano.