Title: Isabel Neville, Duchess of Clarence
Content:  Lady Isabel Neville (5 September 1451 &ndash; 22 December 1476) was the elder daughter and co-heiress of Richard Neville, 16th Earl of Warwick (the Kingmaker of the Wars of the Roses), and Anne de Beauchamp, suo jure 16th Countess of Warwick. She was the wife of George Plantagenet, 1st Duke of Clarence. She was also the elder sister of Anne Neville, who was Princess of Wales by her first marriage and Queen consort of England by her second.
Title: Isabel Neville, Duchess of Clarence
Content:  Isabel Neville was born at Warwick Castle, the seat of the Earls of Warwick, on 5 September 1451. On 11 July 1469, Isabel secretly married George Plantagenet, 1st Duke of Clarence, the younger brother of Edward IV in Calais. The marriage was arranged against the King's wishes by her father, and the ceremony was conducted by Isabel's uncle George Neville, archbishop of York. Following their marriage, Clarence joined forces with Warwick and allied with the Lancastrians led by Margaret of Anjou, queen consort to Henry VI. After Isabel Neville's sister Anne was married to Edward of Westminster, Prince of Wales, the son and heir of Henry VI, Clarence rejoined his brother, realizing that it was now unlikely that he would become king. Letters, from King Edward, were taken to Clarence by an unnamed lady who came to visit Isabel before Warwick and Clarence invaded England for the Lancastrians in September 1470. Inside these letters were promises of reconciliation from the king if Clarence abandoned the cause of Warwick and the Lancastrians. Clarence replied that he would join King Edward as soon as was conveniently possible.
Title: Isabel Neville, Duchess of Clarence
Content: No name (c. 17 April 1470), born outside Calais. Died at sea. ; Identified by some sources as a girl named Anne, and by others as an unnamed boy. ; Margaret Pole, 8th Countess of Salisbury (14 August 1473 – 27 May 1541). Married Sir Richard Pole; executed by Henry VIII. ; Edward Plantagenet, 17th Earl of Warwick (25 February 1475 – 28 November 1499). Executed by Henry VII for attempting to escape from the Tower of London. ; Richard of Clarence (6 October 1476 – 1 January 1477), born at Tewkesbury Abbey, Gloucestershire, died at Warwick Castle, Warwickshire, buried Warwick. Isabel Neville married George Plantagenet, 1st Duke of Clarence, in Calais, France, on 11 July 1469. Four children resulted:
Title: Isabel Neville, Duchess of Clarence
Content:  Isabel Neville died on 22 December 1476, two and a half months after the birth of Richard. It is now thought the cause was either  consumption or childbed fever, yet at the time her husband accused one of her ladies-in-waiting of having murdered her, and committed in his turn a notorious judicial murder of the lady, called Ankarette Twynyho. Ankarette's grandson Roger Twynyho received from Edward IV a full retrospective pardon for Ankarette, and the petition he submitted to the king in 1478 describes fully the circumstances of the case, well illustrating the quasi-kingly high-handedness of Clarence, which was ultimately not tolerated by 
Title: Isabel Neville, Duchess of Clarence
Content:  consideration of the imaginations of the said duke and his great might, the unlawful taking of the said Ankarette through three several shires, the inordinate hasty process and judgement, her lamentable death and her good disposition, the king should ordain that the record, process, verdict and judgement should be void and of no effect, but that as the premises were done by the command of the said duke the said justices and sheriff and the under-sheriff and their ministers should not be vexed. The answer of the king was: Soit fait comme il est désiré ("Let it be done as the petitioner requests")".
Title: Isabel Neville, Duchess of Clarence
Content:  after the closing of Pasche [i.e. Easter], and then caused her to be brought to the Guildhall at Warwick before divers of the justices of the peace in the county then sitting in sessions and caused her to be indicted by the name of Ankarette Twynneowe, late of Warwick, widow, late servant of the duke and Isabel his wife, of having at Warwick on 10 October, 16 Edward IV., given to the said Isabel a venomous drink of ale mixed with poison, of which the latter sickened until the Sunday before Christmas, on which day she died, and the justices arraigned the said 
Title: Isabel Neville, Duchess of Clarence
Content:  and a jury appeared and found her guilty and it was considered that she should be led from the bar there to the gaol of Warwick and from thence should be drawn through the town to the gallows of Myton and hanged till she were dead, and the sheriff was commanded to do execution and so he did, which indictment, trial and judgment were done and given within three hours of the said Tuesday, and the jurors for fear gave the verdict contrary to their conscience, in proof whereof divers of them came to the said Ankarette in remorse and asked her forgiveness, 
Title: Isabel Neville, Duchess of Clarence
Content:  king: "That whereas the said Ankarette on Saturday, 12 April, 17 Edward IV [i.e.1477], was in her manor at Cayford [i.e. Keyford, Somerset] and Richard Hyde late of Warwick, gentleman, and Roger Strugge late of Bekehampton, co. Somerset, towker, with divers riotous persons to the number of fourscore by the command of George, duke of Clarence, came to Cayforde about two of the clock after noon and entered her house and carried her off the same day to Bath and from thence on the Sunday following to Circeter [i.e. Cirencester], co. Gloucester, and from thence to Warwick, whither they brought her on the 
Title: Isabel Despenser, Countess of Warwick
Content:  a child. ; 5) Anne de Beauchamp, who became 16th Countess of Warwick, following the deaths of her brother and his infant daughter. Anne married Richard Neville, the Kingmaker, eldest son of Richard Neville, 5th Earl of Salisbury, and who became jure uxoris 16th Earl of Warwick. Her husband therefore was the brother of her own brother's wife. They had two daughters who married at the highest level: Isabel Neville (1451–1476), who married George Plantagenet, 1st Duke of Clarence (1449–1478), and Anne Neville (1456–1485), who married firstly Edward of Westminster, Prince of Wales, and secondly King Richard III (1483–1485). Isabel married twice, successively to two identically named first-cousins, grandsons of Thomas de Beauchamp, 11th Earl of Warwick:
Title: House of Neville
Content:  brothers: Richard, Duke of Gloucester, and Clarence, who had returned to the family fold before the Battle of Barnet. Clarence, whose claim was founded on his marriage to Isabel Neville, gained the earldoms of Warwick and Salisbury. Gloucester acquired the old Neville estates in the north, establishing his claim by marrying Anne Neville, who had been widowed by Prince Edward's death in the final Lancastrian defeat at the Battle of Tewkesbury in 1471. The northern lands and clientage inherited from the Nevilles became Gloucester's main powerbase, and he adopted Middleham Castle as his principal residence until his usurpation of the throne as Richard III in 1483. Reflecting the estrangement between the two branches of the family, the Nevilles of Raby, headed by Ralph Neville, Earl of Westmorland, had sided with 

Question: Who is the mother of Isabel Neville, Duchess of Clarence?
Answer: Anne Neville, 16th Countess of Warwick.