Sarah Hill Brick Wall

Sarah Hill married my convict ancestor, John Devonald in 1847 in Newcastle NSW in the Presbyterian church. She was widowed in 1856 and remarried in 1857 to James Laughton. She dies in Newcastle in 1901. She had no children, (I'm a descendant of John Devonalds sister.)
I would like to know about her background if possible? She would have been born in the early 1820's but I don't know where, who her parents were, why she came to Australia (she paid her own passage) and when she arrived in NSW. Possible options are 1842 on the Wilmot or 1846 on the Hamlet, but I have not been able to confirm either.
Who was she? Was she Scottish as suggested by her commitment to the Presbyterian church? A newspaper article from c. 1845 in the Newcastle area rrefers to a Sarah Hill (possible her, but not confirmed) as being Irish.
She is a mystery. All official records of her in Nsw make no reference to her date or place of birth or parents names.
She also travelled to San Francisco in about 1851. I have a shipping record of her return to NSW with John Devonald. Did they go there in pursuit of gold?
Any suggestions welcome!