VCH Huntingdon, VOL 3, pp. 22-26 identifies Amice LE STRANGE as the widow of Richard FITZ SIMON, of Dunmow, Essex and Pensthorpe, Norfolk:
http://www.british-history.ac.uk/vch/hunts/vol3/pp22-26
A pedigree of the FITZ SIMON family can be found in ‘Memorials, Archaeological and Ecclesiastical of the West Winch Manors…’, p. 77, by George Eller (1861):
https://books.google.co.uk/books?id=MKYLAAAAYAAJ&pg=PA77&dq=
Amice does not feature in the above pedigree, nor is mentioned in ‘Le Strange Records’, by Hamon Le Strange (1916).
She is revealed to have been the sister of Fulk LE STRANGE, 1st Baron Strange of Blackmere in SC 8/123/6115:
http://discovery.nationalarchives.gov.uk/details/r/C9208285
Apologies if this has been previously discussed, I did not find any messages on the topic in the group’s archives.
Will Acton