Alice had died before the 1851 census, yet had a daughter Mary Ann in Q3/1850. Birth were recorded at Bury, so this is most likely the death record
MATHER, ALICE 32 GRO Reference: 1851 M Quarter in BURY LANCASHIRE Volume 21 Page 257
Name: Alice Mather Gender: Female Birth Date: 1818 Death Date: Feb 1851 Death Place: Whitefield, Metropolitan Borough of Bury, Greater Manchester, England Cemetery: St. Mary the Virgin Churchyard Burial or Cremation Place: Prestwich, Lancashire Has Bio?: Y Spouse: Robert Mather URL: https://www.findagrave.com/memorial/223140942/alice-mather
Alice and Robert were married in a religious ceremony on October 3rd, 1836 in Oldham.4 They had two sons and four daughters, named Jesse, Richard, Nancy, Eliza, Margaret and Mary. There are no more children.
Name: Eliza Mather Baptism Date: 6 Jan 1842 Parish: Prestwich, Lancashire, England Father: Robert Mather Mother: Alice Mather Register Type: Bishop's Transcripts Reference Number: Drm/2/263
Aged 5 in 1851, born Whitefield Full age in 1867 when married (and Matthew was 20)
Name: Margaret Mather Baptism Date: 15 Mar 1846 Baptism Place: Prestwich, St Mary, Lancashire, England Father: Robert Mather Mother: Alice Mather Reference Number: L160/1/3/5 Item Number: 2 Archive Roll: 591
MATHER, RICHARD WHITWORTH GRO Reference: 1848 M Quarter in BURY, LANCASHIRE Volume 21 Page 331
Name: Richard Mather Baptism Date: 11 Jun 1848 Parish: Prestwich, Lancashire, England Father: Robert Mather Mother: Alice Mather Register Type: Bishop's Transcripts Reference Number: Drm/2/263
MATHER, MARY ANN WHITWORTH GRO Reference: 1850 S Quarter in BURY LANCASHIRE Volume 21 Page 359
Name: Mary Ann Mather Gender: Female Baptism Date: 20 Oct 1850 Baptism Place: Prestwich, Lancashire, England Father: Robert Mather Mother: Alice FHL Film Number: 1545724