1851UKC Jacob Jenkins & family; Wales > Monmouthshire > Mynyddyslwyn > District 3c; Penmaen, Monmouth; image 28 of 40 @ancestry.com; Source information: HO107/2453; Registration district: Newport; Sub-registration district: St Woollos; ED, institution, or vessel: 3c; Folio: 445; Page: 30; Household schedule number: 98; GSU Number: 104194; “Crumlin”

1861UKC Jacob Jenkins & Fam; Wales Census > Monmouthshire > Mynyddyslwyn > District 6; image 10 of 39 @ancestry.com - no Mercy wife listed but 1st 3 children same as on 1851 sample
Jacob Jenkins, HOH, b. 1820 in Mynyddyslwyn, Monmouthshire, Wales
John Jenkins, Son, b. 1845 in Mynyddyslwyn, Monmouthshire, Wales
Martha Jenkins, Daughter, b. 1848, in Mynyddyslwyn, Monmouthshire, Wales
Margret Jenkins, Daughter, b. 1851 in Mynyddyslwyn, Monmouthshire, Wales
Mercy Jenkins, Daughter, b. 1853 in Mynyddyslwyn, Monmouthshire, Wales
Harriet Jenkins, Daughter, b. 1856 in Mynyddyslwyn, Monmouthshire, Wales

could this be her living with Abraham & Gwenllian???? (says serv not niece)
POSS 1871UKC Wales Census Monmouthshire Mynyddislwyn District 6; image 34 of 47 @ancestry.com; Source Citation; Piece: 5352; Folio: 136; Page: 33
Source Information; Ancestry.com. 1871 Wales Census [database on-line]. Provo, UT, USA: Ancestry.com Operations Inc, 2004.
Civil Parish: Mynyddislwyn
Ecclesiastical parish: Penmaen
County/Island: Monmouthshire
ED, institution, or vessel: 6
Household schedule number: 188
Piece: 5352; Folio: 136; Page Number: 33
Household Members:
Abraham Jenkins 66 green grocer
Quenllian Jenkins 60
Abraham Jenkins 22
Isaac Jenkins 15
Margaret Jenkins 20 dom servant b 1851 Mynyddislwyn