The mother is Harriet A. Staveley:
The engagement was announced 25 Oct 2005, between Benjamin W.R. Thorpe,
only son of Mr & Mrs Gerald Thorpe, of Northwood, Middlesex, & Harriet
A. Staveley, scion of that BLG family, eldest daughter of the late
Simon Staveley, and Mrs Simon Staveley, of Ripon, North Yorkshire.
Source: YP 25 Oct 2005
https://groups.google.com/forum/#!msg/alt.talk.royalty/WBY8qtpyxY4/kunYsXecwzMJ
about Harriet Therese Norrie STAVELEY-HILL:
Mr W.H. Wright-Morris and Miss H.T.N.d'A. Staveley-Hill
The engagement is announced between William, son of Mr
Roger Wright-Morris, of Chacewater, Cornwall, and Mrs Sonia
Wright-Morris, of Hammersmith, London, and Harriet, elder daughter of Mr
and Mrs Henry Staveley-Hill, of Langton Matravers, Dorset.
http://announcements.telegraph.co.uk/engagements/51760/mr-w.h.-wright-morris-and-miss-h.t.n.d%27a.-staveley-hill