Her daughter, Jeanne (we know her as Joan of Arc), claimed to have visions that inspired her to get involved in the Hundred Years War and the French civil war that prevented the Dauphin (son of Charles VI) to be enthroned. Jeanne's involvement helped the Dauphin become Charles VII. Unfortunately, that made Jeanne many enemies, and she was eventually captured and put on trial for (among other things) heresy, after which she was burned at the stake.
Jeanne's father died shortly after, some say of grief. Isabelle had a different reaction: she would fight to clear her daughter's name. Isabelle moved to Orléans, where a city grateful for her daughter's work offered Isabelle a pension.
Her first move was to send a petition to Pope Nicholas V to re-open the case. An inquiry was begun in 1449, and the chief inquisitor of heresy in France took it on in May 1452. Investigations dragged on, and Isabelle went to Paris to speak to the new pope, Calixtus III. Calixtus gave the chief inquisitor, Jean Bréhal, his support and three assistants. Bréhal presided over the re-trial in November 1455, at which the 70-year-old Isabelle gave a moving speech. 115 witnesses were questioned (many of whom had been part of the first trial). Bréhal declared in June 1456 that Jeanne had died a martyr, and he posthumously excommunicated the had of the original trial, Bishop Pierre Cauchon, as a heretic who pursued a secular vendetta. Calixtus confirmed the excommunication.
The illustration above shows Isabelle and two of her children kneeling in the lower right, facing Jean Bréhal dressed as a Dominican, with the pope and others presiding. Bréhal wrote two books about his investigations and the retrial. He was present at a public burning of the articles of the original trial.
A victorious Isabelle died on 28 November 1458.
There is another member of the family that we know about: Jeanne's brother, Pierre. Why more information about him has made it to the historical record is not necessarily commendable, however. Little brothers can be annoying, and Jeanne's little brother did something selfish and bad. I'll explain next time.