From the FMG Medieval Lands database:

daughter of Hildouin IV de Montdidier (Ramerupt) and Adelaide de Roucy:

BEATRIX de Ramerupt (-2 Sep after 1129). The Chronicle of Alberic de Trois-Fontaines names "Beatrix" as second daughter of Ebles Comte de Roucy and incorrectly names her husband "Rotroldo comiti de Pertico"[1076]. The Genealogiæ Scriptoris Fusniacensis names "comitis Hilduini de Rameruth maior natu filia dicta Beatrix" as wife, also incorrectly, of "Rotaldo comiti de Pertica"[1077]. She is named as wife of Geoffroy Comte du Perche by Orderic Vitalis, incorrectly saying that she was daughter of "the count of Rochefort"[1078] and specifying in another passage that her son Rotrou was consanguineus of Alfonso I King of Aragon[1079].

m GEOFFROY de Châteaudun, son of ROTROU Vicomte de Châteaudun, Comte de Mortagne & his wife Adelise de Bellême (-mid-Oct 1100, bur Nogent-le-Rotrou[1080]). He succeeded his father in [1080] as Comte de Mortagne. He adopted the title Comte du Perche after 1090.

Comte Geoffroy & his wife had five children:

a) ROTROU "le Grand" du Perche (-killed in battle Rouen [20 Jan/23 Apr] or 6 May 1144). He is named and his parentage given by Orderic Vitalis[2155]. "Beatrice uxor mea et filio meo Rotroco nec non fratribus meis" confirmed the confirmation of donations to Saint-Denis de Nogent by "Gaufridus castri Mauritaniæ comes" dated [1080][2156]. He succeeded his father as Comte du Perche.

b) MARGUERITE du Perche (-27 Aug after 1156). She is named and her parentage given in Orderic Vitalis, who also names her husband and, in a later passage, her father and two older sons[2157]. The Genealogiæ Scriptoris Fusniacensis names " Rotaldum eiusdem loci comitem et Iulainam de Aquila matrem regine Navarrensis, et Margaretam uxorem Gisleberti de Novo-burgo" as children, incorrectly, of "Rotaldo comiti de Pertica" & his wife Beatrix de Roucy, specifying that Marguerite had children "Rotaldum Ebrodiensem episcopum cum aliis liberis utriusque sexus"[2158]. “Henricus…Warwicense consul et Margareta uxor mea et Rogerus noster filius” donated property to Warwick St Mary by undated charter[2159]. The 1130 Pipe Roll records "comitisse de Warwic" in Wiltshire[2160]. 1156. The necrology of the church of Evreux records the death "27 Aug" of "Margarita mater Rotrodi episcopi"[2161]. m HENRI de Beaumont Earl of Warwick, son of ROGER Seigneur de Beaumont-le-Roger & his wife Adeline de Meulan ([1048]-[20 Jun] 1119, bur Préaux).

c) JULIANA du Perche (-after 1132). She is named and her parentage given in Orderic Vitalis, who also names her husband[2162]. The Genealogiæ Scriptoris Fusniacensis names "Rotaldum eiusdem loci comitem et Iulainam de Aquila matrem regine Navarrensis, et Margaretam uxorem Gisleberti de Novo-burgo" as children, incorrectly, of "Rotaldo comiti de Pertica" & his wife Beatrix de Roucy, specifying that Marguerite had children "Rotaldum Ebrodiensem episcopum cum aliis liberis utriusque sexus"[2163]. "Rotrocus comes Perticensium" donated property to the abbey of Sainte-Trinité de Tiron by charter dated [1119] subscribed by "Juliane soror mea, Richerii filius eius"[2164]. "Juliane soror mea" witnessed the charter dated [1120] under which "Perticensis comes Rotrocus" donated property to the abbey of Sainte-Trinité de Tiron[2165]. "Domine Juliane" recognised rights of Saint-Denis de Nogent by charter dated to [1122/33], specifying that she was governing Perche while the count was absent in Spain, witnessed by "Gislebertus puer filius prefate Juliane"[2166]. m GILBERT Seigneur de Laigle, son of RICHER de Laigle & his wife Judith d'Avranches (-[1118]).

d) MATHILDE du Perche (before 1100-27 May 1143, bur Arnaco). The Chronicon Gaufredi Vosiensis records the marriage of "Guidonem", son of "Gerardus", and "Matilde, matre Bosonis de Torena quæ Arnaco condita est"[2167]. In another passage, the Chronicon Gaufredi Vosiensis records that "Raymundus" married "Mathilde…soror Comitis de Pertico"[2168]. The Chronicon Gaufredi Vosiensis records the death "V Kal Jun" of "Mathildis uxor quondam Raymundi de Torenna" and her burial by "Guidone…Crassus viro suo filio Geraldi de Turribus" at "Arnaco", recording that her son Boson was killed within one month of his mother's death[2169]. m firstly RAYMOND [I] Vicomte de Turenne, son of BOSON [I] Vicomte de Turenne & his wife Gerberge ---. 1127. m secondly GUY [IV] "le Gros" de Lastours, son of GERARD [I] de Lastours & his wife Humberga --- (-Jerusalem [1147/49]).

e) daughter . The primary source which confirms her parentage has not yet been identified.

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Geoffrey du Perche et Mortaigne I, died 1100. He was the son of 12. Rotrou de Chateaudun I and 13. Adeline Domfront. He married 7. Beatrice de Montdidier.

7. Beatrice de Montdidier She was the daughter of 14. Hildouin de Montdidier and 15. Alice de Roucy.

Children of Geoffrey Mortaigne and Beatrice de Montdidier are:

 i. Julienne du Perche, married Gilbert l'Aigle 1091; born Bef. 1047.

3 ii. Mahaut du Perche, born Bet. 1100 and 1105 in Perche, Normandy, France; died 18 May 1143; married Raymond de Turenne I 1122.
iii. Margaret du Perche, born Abt. 1045; died Abt. 1136; married Henry de Beaumont de Newburgh Bef. 1100 in Perche, Normandy, France; born 1045 in Neubourg, Manche, France; died 1123 in Pontaudemer, Normandy, France.

Beatriz de Roucy, era hermana de Felicia de Roucy, segunda esposa del rey Sancho Ramírez de Aragón y madre de Pedro I y Alfonso I el Batallador. Por tanto, Margarita era sobrina segunda de ambos monarcas navarro-aragoneses. Asimismo, era sobrina del conde Rotrou III de Perche (1100-1144), hermano de su madre y colaborador de Alfonso I en la reconquista del valle del Ebro, que desde 1123 estaba al frente del distrito de Tudela.