The info on her marriage certificate would be more reliable than a death, and you will also get her mother's maiden surname.
It appears that it was Owen DONNELLY and Margaret having children in Campbelltown in the 1840's/1850's.They were probably the couple who arrived in 1842 on the 'William Sharples' from Co. Louth.Margaret was pregnant and gave birth onboard, but the baby died.They had no other children with them. Owen was born c1818 and that sits quite well with the Owen DONNELLY who died at Campbelltown in 1886 aged 66.His death cert should list all his children.
The Bounty immigrants index cards are on FamilySearch. https://familysearch.org/pal:/MM9.3.1/TH-267-11587-12892-61?cc=1542665&wc=M99P-BTF:1041274289
Very difficult to read the original but I think Margaret's parents were Peter and AnnE KEDDY.The baptism of Owen and Margaret's son John has her name as KENNEDY.So who knows!!