On the 1842 marriage cert you now have: do the witnesses appear to be related to Eliza?
Also, where was Eliza living when she married? Sometimes those details can offer further clues when researching an ancestor.
The handwriting is hard to make out the names. I think its Isaac ...... and Elizabeth Pith?
It does state they were living at 19 Kent Street?
John James was a Mariner, his father John James was a joiner.
They were married at St Micheals Church in Liverpool,.
Their 2 older children were born in Liverpool, with the first not long after they were married. The othere were born in Penzance, Cornwall.
It makes sense they married in Liverpool. They were full age at time of marriage