Round explained this in *Feudal England* (1909) pp 475-476, here:
Apart from the proofs he gave, we know from Daventry priory charters
that the daughter of Simon de St Liz and Matilda (later wife of David I
of Scotland) married successively Robert fitz Richard and Saher de
Quincy - in the edition by Michael Franklin (1988), pp. 3-4 no. 8
("Matillda de Senliz ... notificetur me concessisse et in perpetuam et
liberam elemosinam dedisse deo et ecclesie sancti Augustini de Davintre
et monachis ibidem deo servientibus ... pro anima domini mei Roberti
filii Ricardi ... et viii acras de dominio meo iuxta terram quam regina
Matillda mater mea illis dedit") and p. 2 no. 5 ("Seiherus de Quinci et
Matilda de Senliz uxor eius ... Notum sit ... nos in perpetuam
elemosinam dedisse deo et ecclesie sancti Augustini de Daventre et
monachis ibidem deo servientibus ... viii acras de dominio nostro iuxta
terram quam regina Matilda illis dedit"). Both of these were ascribed
the date range 19 December 1148/27 December 1166 by Franklin.
This Matilda last occurs in an entry under Essex & Hertfordshire in the
pipe roll for 1154 ("Et Matildi . de Seinliz .vii. s.") and she died not
long afterwards since she was recorded as deceased in an extant
mid-12th-century original document, Daventry charters as above p. 39 no.
113 ("Matilde de Seinliz quondam domina de Daventre").
Her namesake daughter who used her surname had the happiness to be aged
both 50 and 60 decades later, in 1185, when she was recorded twice in
'Rotuli de dominabus', here p. 1:
"Norfolk" in note 2 is a mistake for Suffolk), and here p. 63: