Ann (i.e. Nancy) died after 1790. The only Nancy Mather buried at St Nicholas was the daughter of Henry and Elizabeth. There are three Ann Mather burials in 1796, 1806 and 1846, so assuming Richard and Ann are buried at St Nicholas, only the 1806 burial is possible.
Ann Mather
Birth unknown
Death 1806
Burial St. Nicholas' Churchyard, Liverpool, Metropolitan Borough of Liverpool, Merseyside, England
Memorial ID 224512488
Name Ann Mather
Birth Date abt 1745
Burial Date 3 Aug 1806
Death Age 61
Parish Liverpool, St Nicholas, Lancashire, England
Father's Name Richard Mather
Register Type Bishops Transcripts
Reference Number Drl/2/80
Ann, Relict of Richard Mather, of Crosbie Street, Rigger
NOTE: There is also a burial 1 July 1802 for Ann Tyrer aged 56 at Liverpool St Nicholas, but this is another.