ANY SUGGESTIONS?

I am hoping someone somewhere can offer a reasonable explanation for the following:-

Robert Smith born 1824 married Jane Whinham 24 Nov 1844 in Hexham where both of them resided, both of full age Robert was a bachelor Jane a spinster, Robert was a gardener and his father Robert was a gardener. So far so good! and all correct from what was known about the Smith family. Jane gives her father as William a labourer.

Various children followed I have all the certs on every one names of children, dates, Father, Fathers occupation is correct. Mothers name..... Jane Smith formerly FISHER.  HELP where did Fisher come from?

Now more  confusion

1841 CENSUS                             Cockshaw Hexham                                                                                                                                                                                                                                

Robert Smith     45   Gardener                                                                                                                  Joseph Farley         65     Sailor

Mary Smith       45                                                                                                                                   Margaret Farley     50      Lodging House Keeper

Robert Smith     15  Labourer

William Smith    15 Labourer

John Smith        10

Simpson Smith     5   

Could not find Jane Fairley or Farley.

1851 CENSUS

Peggy Fairley         Head           Widow          61    Lodging House Keeper

Robert Smith   Son in Law   Mar   27   Gardener Journeyman

Jane Smith    Daur   Mar   31    wife

Mary Smith    Gd Daughter    4

Robert Smith    Gd Son    2  Scholar

Alice Fisher    Gd Daughter    7    scholar

Jeremiah Fisher   Nephew    44   Tailor Journeyman

Alice Fisher is the child of Mary Ann Fisher not Jane Fisher.

So the problem, Jane on the 1851 census is Peggy Fairley's daughter, so I expect Peggy was Peggy Fisher and married Joseph Fairley, so she is now Peggy Fairley  Jane on all the Birth certs of her children is Jane Fisher, So why did she marry with the name Jane Whinham ??????