Is this the marriage entry you found (Lancashire Online Parish Clerk)

Marriage: 17 Jul 1831 St Peter, Liverpool, Lancashire, England
Benjamin Mostyn - (X), Labourer of This Parish
Elizabeth Woods - (X), Spinster of This Parish

Witness: Thomas Sutton; Ann Moore, (X)Married by Banns by: Jno. Robinson, Curate
Register: Marriages 1831 - 1833, Page 57, Entry 169

Source: LDS Film 93919

She's not down as a minor so her birth date could be around 1810. The 1822 suggestion from the the 1871 census might be pushing it a bit! Too bad they don't give father's names. I don't know how you progress from here. If one of the other censuses gave her birth parish it might be a help. Do you know when she died or where she is buried? Hopefully someone else reading will have suggestions.