Eleanor's year of birth is not known precisely: a late 13th-century genealogy of her family listing her as 13 years old in the spring of 1137 provides the best evidence that Eleanor was perhaps born as late as 1124. On the other hand, some chronicles mention a fidelity oath of some lords of Aquitaine on the occasion of Eleanor's fourteenth birthday in 1136. This, and her known age of 82 at her death, make 1122 more likely the year of birth. Her parents almost certainly married in 1121.
Inheritance
In 1137 Duke William X left Poitiers for Bordeaux and took his daughters with him. Upon reaching Bordeaux, he left them in the charge of the Archbishop of Bordeaux, one of his few loyal vassals. The duke then set out for the Shrine of Saint James of Compostela in the company of other pilgrims. He died, however, on Good Friday of that year (9 April).  Eleanor, aged twelve to fifteen, then became the Duchess of Aquitaine, and thus the most eligible heiress in Europe. As these were the days when kidnapping an heiress was seen as a viable option for obtaining a title, William dictated a will on the very day he died that bequeathed his domains to Eleanor and appointed King Louis VI of France as her guardian. William requested of the king that he take care of both the lands and the duchess, and find her a suitable husband. However, until a husband was found, the king had the legal right to Eleanor's lands. The duke also insisted to his companions that his death be kept a secret until Louis was informed; the men were to journey from Saint James of Compostela across the Pyrenees as quickly as possible to call at Bordeaux to notify the archbishop, then to make all speed to Paris to inform the king.  The king of France, known as Louis the Fat, was also gravely ill at that time, suffering from a bout of dysentery from which he appeared unlikely to recover. Yet despite his impending death, Louis's mind remained clear. His heir, Prince Louis, had originally been destined for the monastic life of a younger son but had become the heir apparent when his older brother, Philip, died from a riding accident in 1131.  The death of William, one of the king's most powerful vassals, made available the most desirable duchy in France. While presenting a solemn and dignified face to the grieving Aquitainian messengers, Louis exulted when they departed. Rather than act as guardian to the duchess and duchy, he decided to marry the duchess to his 17-year-old heir and bring Aquitaine under the control of the French crown, thereby greatly increasing the power and prominence of France and its ruling family, the House of Capet. Within hours, the king had arranged for Prince Louis to be married to Eleanor, with Abbot Suger in charge of the wedding arrangements. Prince Louis was sent to Bordeaux with an escort of 500 knights, along with Abbot Suger, Theobald II, Count of Champagne, and Count Ralph.

Q: What was her inheritance?
A: became the Duchess of Aquitaine,

Q: What else can you tell me about her inheritance?
A: As these were the days when kidnapping an heiress was seen as a viable option for obtaining a title,

Q: So there was a fear she would be kidnapped?
A: The duke also insisted to his companions that his death be kept a secret
Why is that?
Rather than act as guardian to the duchess and duchy, he decided to marry the duchess to his 17-year-old heir
Rather than act as guardian to the duchess and duchy, he decided to marry the duchess to his 17-year-old heir