Her birth cannot be identified, though there was one Frances S Smyth born in 1951 in Birminghma, though a tad young.

In 2020 Mike Walton wrote to say that hsi uncle’s wife Sally had died in 2019.
No entry on the will index nor on FindMyPast’s death index nor on the GRO death index.
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The marriage looks very much to have been this:

First name(s) OLIVER
Last name POWYS
Marriage quarter 2
Marriage year 1967
MarriageFinder™ OLIVER POWYS married
Frances S Smyth
Spouse's last name Smyth
District Richmond upon Thames
County Surrey
Country England
Volume 5D
Page 1426
Record set England & Wales Marriages 1837-2005
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