She still had some land, and was not left destitute or alone. On 20 January 1214, she married the 2nd Earl of Essex, Geoffrey FitzGeoffrey de Mandeville, still a young man in his 20s. Geoffrey was an opponent of King John during the Barons War. John saw fit to charge Geoffrey 20,000 marks for the privilege of marrying Isabella and gaining her inheritance and the title Earl of Gloucester.
Geoffrey himself was on his second marriage when it came to Isabella. He had been married to Matilda, daughter of a leader of John's opponents in the hostilities leading up to the Magna Carta, Robert Fitzwalter. Matilda died young and childless. Geoffrey did not last long as a husband: he died on 23 February 1216, wounded fatally during a tournament.
Isabella did not remain single for very long. The Chief Justiciar of England, Hubert de Burgh, was widowered, and open to remarriage. Coincidentally (?), Hubert was also having trouble getting along with the king, this time John's son Henry. They married in September 1217. Isabella, who was in her 50s, died only a month later. Her name is listed in the obituary lists of deceased nobles at Canterbury Cathedral, but her final resting place is unknown.
We've been talking about nobles and marriages and conflict with kings. Let's shift to another type of conflict, mentioned in paragraph three above: how dangerous were tournaments? That's for next time.