Some clues:
William Kneale was a widower aged 33 in 1851. There is a burial record in Malew in 1853 for a 34 year-old William, suggesting that Eliza was an only child and an orphan at age 10 or 11.
John and Jane Parry have a nephew, but no child of there own at home in 1851 (High Street Bangor - HO107/2518 folio 129 p 9) and I found no Manx Eliza Parry in Wales.
There is a Castletown born Eliza Nicholes in Caernarvon in 1871, presumably Eliza #2.
I do not know if there are any adoption or foster home records to support this.