Could this be her from the 1871 census?
RG10; Piece: 5724; Folio: 105; Page: 11
Llanddona, Anglesey
William Thomas 56 Ag Lab Llanddyfnan, Anglesey,
Mary Thomas 45 Penrhoslligwy, Anglesey
William Thomas 24 Ag Lab Llanddona, Anglesey
Catherine Thomas 16 Sew at home Llanddona, Anglesey
Benjamin Thomas 12 Llanddona, Anglesey