I see Elizabeth A. in 1901 had a Whitmore staying with her in the household
Lucy Whitmore 14 Wilden, Bedfordshire, Sister-in-law
The only Lucy Whitmore I can see who this might be in 1891 is
RG12 1253 folio 60
East End Wilden Bedfordshire
Whitmore, Lucy 42 Wilden, Bedfordshire, Head Single Charwoman
Whitmore, Sarah 17 Wilden, Bedfordshire, Daughter
Whitmore, Thomas 13 Wilden, Bedfordshire, Son
Whitmore, Eliza 11 Wilden, Bedfordshire, Daughter
Whitmore, Annie 8 Wilden, Bedfordshire, Daughter
Whitmore, Lucy 6 Wilden, Bedfordshire, Daughter
Whitmore, Walter 3 Wilden, Bedfordshire, Son
1881 RG11 1625 folio 77
2 Church Row, Wilden, Bedfordshire
Lucy Whitmore 32 Bolnhurst, Bedfordshire, Housekeeper (Head) Unmarried Lacemaker
William Whitmore 9 Wilden, Bedfordshire, Son
Sarah J. Whitmore 6 Wilden, Bedfordshire, Daughter
Thomas Whitmore 3 Wilden, Bedfordshire, Son
Eliza Whitmore 11 Wilden, Bedfordshire, Daughter
'Housekeeper' to William Fuller and his 9 year old daughter
1871 census RG10 1537 folio 54
15 High Road Bolnhurst Bedfordshire
William Whitmore 18 Bolnhurst, Bedfordshire, Head Unmarried
Lucy Whitmore 20 Bolnhurst, Bedfordshire, Sister Unmarried
Elizabeth A Whitmore 2 Bolnhurst, Bedfordshire, Niece
Alice Whitmore 16 Bolnhurst, Bedfordshire, Niece
It therefore seems a possibility that Elizabeth A was Lucy's first child and is the 11 year old Eliza of the 1881 census? The Lucy on the census of 1901 - given as her sister-in-law, in modern term usage would be a step sister or in this case a half sister i.e. a sister-in-law but not a full sister.
1861 census RG9 985 folio 58
Street Bolnhurst Bedfordshire
Samuel Whitmore 54 Thurleigh, Bedfordshire, Head Married Ag lab
Jane Whitmore 51 Great Staughton, Huntingdonshire, Wife Married lacemaker
Sophia Whitmore 28 Keysoe, Bedfordshire, Daughter Lacemaker
Ann Whitmore 25 Keysoe, Bedfordshire, Daughter Lacemaker
Joseph Whitmore 23 Bolnhurst, Bedfordshire, Son Ag lab
Emmanuel Whitmore 19 Bolnhurst, Bedfordshire, Son Ag lab
Thomas Whitmore 15 Bolnhurst, Bedfordshire, Son Ag lab
Lucy Whitmore 12 Bolnhurst, Bedfordshire, Daughter Lacemaker
William Whitmore 8 Bolnhurst, Bedfordshire, Son
Alice Whitmore 7 Bolnhurst, Bedfordshire, Daughter
George Whitmore 4 Bolnhurst, Bedfordshire, Son
Lewis Whitmore 3 Bolnhurst, Bedfordshire, Daughter
Harriet Whitmore 1 Thurleigh, Bedfordshire, Daughter
Next door James Whitmore aged 57 born Bolnhurst and his wife born Keysoe and their son.
1901 census RG13 1495 folio 19
Village Wilden Bedfordshire
Lucy Whitmore 52 Bolnhurst, Bedfordshire, Head Single Charwoman
Walter Whitmore 12 Wilden, Bedfordshire, Son
Regards
Valda