Lady Louisa Dunsany is the wife of Lord William Dunsany, master of Helwater. By the late 1750s, they were impoverished aristocrats who sought suitable marriages for their two remaining children, Geneva and Isobel.
Louisa and her husband William had three children. Their eldest, Gordon Dunsany, was killed in the Battle of Prestonpans. After this loss, they devoted that much more upon their daughters, Geneva and Isobel. After the Jacobite Rising of 1745, their estate, Helwater, fell rather heavily into debt.
In 1756, Jamie Fraser arrives at Helwater. The Dunsanys were not made aware of his true identity and are told his name is Alex MacKenzie.
In 1757, the Dunsanys arrange for their eldest daughter Geneva to be married to the wealthy but elderly Lord Ellesmere. Lord Ellesmere provides them 30,000 pounds in exchange for marrying a virgin of good name.
In 1758, Geneva dies in January a few hours after giving birth to a son, William Ransom. The Dunsanys go to Lord Ellesmere's house to take William back to Helwater. Lord Ellesmere is drunk. He knows the baby is not his, but is determined to keep him as his heir. An argument erupts between Lord Ellesmere and Lord Dunsany. Lord Ellesmere grabs William and threatens to drop him out the window if the Dunsanys do not leave. Jamie grabs a pistol and fires at Lord Ellesmere, killing him.
The Dunsanys prevent a scandal by pretending that Jamie was never present in the room, and they presumably instruct the footman, Jeffries, on what to say in the coroner's court. Ultimately, a verdict of "death by misadventure" is returned. In gratitude to Jamie, Lady Dunsany offers to ask Lord John Grey if he can exert his influence to have Jamie released from the conditions of his parole so that he can return home. Jamie replies that he is not ready to return home yet, and Lady Dunsany tells him that he only has to ask.
After the death of their daughter, the Dunsanys dote upon William. In 1764, Lord John Grey weds their remaining daughter, Isobel, and the couple takes on the roles of mother and father to young William.
When Lord John visits Helwater to attend Geneva's funeral, he finds that Lady Dunsany shows great strength in the face of grief, and stands in stark contrast to her husband's diminished state.
Lady Dunsany accompanies Isobel, Mr. Wilberforce, and her young grandson on a picnic. Though they are attended by Isobel's maid and the groom MacKenzie, William manages to wander off into the fog, and there is a brief panic until MacKenzie finds William unharmed.
Lady Dunsany is described as fulsome, but beneath the genial exterior lies a strong will and fortitude. She goes to great lengths to protect her family from scandal in the wake of her daughter's death.
Louisa is a small round woman with faded blonde hair and pale bluish-green eyes. 
- Louisa is the Latinate feminine form of Louis, a French form of Ludovicus, the Latinized form of Ludwig from the Germanic name Chlodovech, which was composed of the elements hlud "famous" and wig "war, battle".
- Dunsany is the name of a title in the Peerage of Ireland, as well as a castle in County Meath. It comes from the Irish Dún Samhnaí.