In 1841 they have a son John, so possibly Dorothy's father:
1841 HO1007/837/27 fol.6 p.7/8
Woodhead, Leemailing, Bellingham
Robert Wilkinson 35 Shepherd
Dorothy " 30
John " 14
Frances " 2
all born in county
and on same page, 4 doors away: 1841 HO107/837/27 fol.7 p.8
Jane Pigg 57 Ag. Lab
Mary " 25
Mary Houmes 60 Ind
all born in county
There's a marriage for a Mary Pigg to John Mewes, 20 Aug 1845, if she was the mother, perhaps she thought it was better for Dorothy to be brought up by her grandparents
1851 Mary & John Mews are in Bellingham with sons Richard 5 & John 3, Mary was born 1813 Falstone
Barbara