Assumed; if correct, this is Mary SCOTT, married 19 Sep 1819 Christchurch (IGI) - but probably not, as according to Pedigree Resource file William’s father was Thomas and he was christened in 1793, not 1786; also, daughter Dianna was born 1815, well before this marriage.
NB Mary gave her place of birth as Salisbury in 1861 census - assuming that this is the same person!