Find Ancestors

To find out someone's mother's name, if one knows their year of birth, and birthplace, to a couple of years, and to a rough area, one puts the information in IGI, including father's name as a bonus, and out pops a suitable candidate.

Putting Isabella's name in gives only:
ISABELLA ASHTON
Christening: 01 APR 1833 Saint Peter, Liverpool, Lancashire, England Father: PETER ASHTON Mother: JANE P020273

which does give Peter as a father, so is Nancy Isabella's sister, not her Mother?

Now entering P020273 in the batch number, entering surname ashton, and father Peter, gives 3 children, one of whom is this:
ANN ASHTON
Christening: 01 DEC 1829 Saint Peter, Liverpool, Lancashire, England Father: PETER ASHTON Mother: JANE P020273

Just that Preston is not Liverpool, and the age for Nancy/Ann is way out.

So, starting new entry in igi for Nancy Ashton, birth 1811 (from 1841 census) +/- 10 years, with father Peter, gives several other possibilities, none actually Preston.

If you can find her in 1851 you will have better idea of area and birthdate.

For background information:
1841 England Census
Isabella Ashton Age: 5 Estimated birth year: abt 1836 Gender: Female Where born: Lancashire, England Civil parish: Preston Hundred: Amounderness County/Island: Lancashire Country: England Registration district: Preston Sub-registration district: Preston
Thos Thompson 60 local
Nancy Ashton 30 local
Isabella Ashton 5
Source Citation: Class: HO107; Piece 499; Book: 8; Civil Parish: Preston; County: Lancashire; Enumeration District: 36; Folio: 7; Page: 9; Line: 13; GSU roll: 306888.

Do you know where they are in 1851, for better age and birthplace information?
Thanks

Nancy Ashton appears on 1841 census in Preston with daughter Isabella. Nancy (Ann) then marries Joseph Whalley in 1845. Her father is named as Peter. How do I go about finding out who her mother was?