Question: Who is the maternal grandmother of Isabel De Verdun, Baroness Ferrers Of Groby?

Knowledge 1: Isabel de Verdun, Baroness Ferrers of Groby
Isabel de Verdun, Baroness Ferrers of Groby (21 March 1317 – 25 July 1349) was an heiress, who was related to the English royal family as the eldest daughter of Elizabeth de Clare, herself a granddaughter of King Edward I of England.When she was a child, Isabel was imprisoned in Barking Abbey, along with her mother and half-sister, after her stepfather had joined the Earl of Lancaster's ill-fated rebellion against King Edward II.Her husband was Henry Ferrers, 2nd Baron Ferrers of Groby. [SEP] Knowledge 2: Elizabeth de Clare
Elizabeth de Clare, 11th Lady of Clare (16 September 1295 – 4 November 1360) was the heiress to the lordships of Clare, Suffolk, in England and Usk in Wales.She was the youngest of the three daughters of Gilbert de Clare, 6th Earl of Hertford and Joan of Acre, and sister of Gilbert de Clare, who later succeeded as the 7th Earl.She is often referred to as Elizabeth de Burgh, due to her first marriage to John de Burgh.Her two successive husbands were Theobald II de Verdun (of the Butler family) and Roger d'Amory.
Knowledge 1: Isabel de Verdun, Baroness Ferrers of Groby
Isabel de Verdun, Baroness Ferrers of Groby (21 March 1317 – 25 July 1349) was an heiress, who was related to the English royal family as the eldest daughter of Elizabeth de Clare, herself a granddaughter of King Edward I of England.When she was a child, Isabel was imprisoned in Barking Abbey, along with her mother and half-sister, after her stepfather had joined the Earl of Lancaster's ill-fated rebellion against King Edward II.Her husband was Henry Ferrers, 2nd Baron Ferrers of Groby. [SEP] Knowledge 2: Matilda of Saxony, countess of Flanders
Matilda of Saxony( c. 935-942 – 25 May 1008) was duchess of Saxony, countess of Saxony, princess of Saxony, and countess of Flanders.She was the daughter of Hermann Billung and Hildegard von Westerburg.She was born in Herzogtum Sachsen, Ostenfrankenreich, now part of modern Germany.Matlida was the sister of Swanhilde of Saxony and Bernard I, duke of Saxony; and half sister of Liudger von Sachsen, Graf von Lesum und Westfalen and Imma Von Billung, Abbess of Hereford.Matilda was the wife of Baldwin III, count of Flanders, with whom she had a son Arnulf II the Young, count of Flanders.After Baldwin's death, Matilda married GodefroiI the Captive, count of Ardennes, with whom she had eleven children: Adelaide d' Ardennes, Duchess of Lorraine; Comte van Verdun Godefroy Herzog von Niederlothringen, II; Gerberge de Verdun, comtesse; Hermann, comte de Verdun et d'Enham; Gothelo I" the Great", duke of Lorraine; Irmgard, comtesse de Verdun; Roger de Verdun, Governor of Ambriences Castle; Frédéric de Verdun; Regilla de Verdun; comte Adalberto Evêque de Vermandois, II and Ermentrude von Lothringen de Verdun.Matilda died on 25 May 1008 and was buried in Ghent, East Flanders, Belgium.
Knowledge 1: Matilda of Saxony, countess of Flanders
Matilda of Saxony( c. 935-942 – 25 May 1008) was duchess of Saxony, countess of Saxony, princess of Saxony, and countess of Flanders.She was the daughter of Hermann Billung and Hildegard von Westerburg.She was born in Herzogtum Sachsen, Ostenfrankenreich, now part of modern Germany.Matlida was the sister of Swanhilde of Saxony and Bernard I, duke of Saxony; and half sister of Liudger von Sachsen, Graf von Lesum und Westfalen and Imma Von Billung, Abbess of Hereford.Matilda was the wife of Baldwin III, count of Flanders, with whom she had a son Arnulf II the Young, count of Flanders.After Baldwin's death, Matilda married GodefroiI the Captive, count of Ardennes, with whom she had eleven children: Adelaide d' Ardennes, Duchess of Lorraine; Comte van Verdun Godefroy Herzog von Niederlothringen, II; Gerberge de Verdun, comtesse; Hermann, comte de Verdun et d'Enham; Gothelo I" the Great", duke of Lorraine; Irmgard, comtesse de Verdun; Roger de Verdun, Governor of Ambriences Castle; Frédéric de Verdun; Regilla de Verdun; comte Adalberto Evêque de Vermandois, II and Ermentrude von Lothringen de Verdun.Matilda died on 25 May 1008 and was buried in Ghent, East Flanders, Belgium. [SEP] Knowledge 2: Charlotte Townshend, Viscountess Townshend
Charlotte Townshend, Viscountess Townshend( died 3 September 1770)," suo jure" 15th Baroness Ferrers of Chartley and 7th Baroness Compton, known as Lady Charlotte Compton until 1749 and as Lady Ferrers of Chartley from 1749 to 1764, was a British peeress.Charlotte was the only surviving child of James Compton, 5th Earl of Northampton, and Elizabeth, 14th Baroness Ferrers of Chartley.The barony of Ferrers of Chartley had fallen into abeyance on her mother's death in 1741.However, in 1749 the abeyance was terminated in Charlotte's favour and she became the 15th Baroness.In 1754 she also succeeded her father in the barony of Compton.In 1751 Charlotte married the Hon. George Townshend, later fourth Viscount Townshend and first Marquess Townshend.When he succeeded in the viscountcy in 1764 she became known as the Viscountess Townshend.Charlotte died in September 1770 and was succeeded in the two baronies by her eldest son George, who was created Earl of Leicester in 1784 and later succeeded as second Marquess Townshend.Her husband survived her by over 30 years and died in 1807.

Answer: Joan of Acre