Isabel de Beaumont ¹

   Another name for Isabel was Isabella of Meulan.

  Research Notes:

From thepeerage.com:
Isabella of Meulan was born between 1102 and 1107.¹ She was the daughter of Robert de Meulan, 1st Earl of Leicester and Elizabeth de Vermandois.² She married Gilbert de Clare, 1st Earl of Pembroke, son of Gilbert fitz Richard and Adeliza de Clermont . She died after 1172.²
As a result of her marriage, Isabella of Meulan was styled as Countess of Pembroke.
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From Wikipedia - Elizabeth of Vermandois :

Isabel de Beaumont (b Aft. 1102), a mistress of King Henry I of England . Married two times:
Gilbert de Clare, 1st Earl of Pembroke by whom she was mother of Richard Strongbow , who invaded Ireland 1170 ;
Hervé de Montmorency, Constable of Ireland (this marriage is not conclusively proven)

Isabel married Gilbert FitzGilbert de Clare 1st Earl of Pembroke, son of Gilbert FitzRichard de Clare and Adelaide de Clermont-en-Beauvaisis. (Gilbert FitzGilbert de Clare 1st Earl of Pembroke was born about 1100 and died on 6 Jan 1148.)