I'm delighted that it has all come together so well for you, and great luck that Lorraine has been watching the BB. She will be able to fill in the Australian gaps for you.
I felt sure that we had the right family when I saw Ann's little sister Isabella aged 7 in the 1871 census when Ann was 12, and her elder sister Jane was 14.
Isabella was bapt 18 Jan.1863, so her birthday would have been very close to the date of Annie Isabella's birthday (bapt 12th January 1878) - maybe even on the same date as Annie Isabella's bapt - and no doubt she was thrilled with the new baby.
When 1800s birth dates have been found from MIs, family bibles, and the occasional parish reg entry, they were usually only a few days before the bapt date, unless recorded with an older age in the parish register.
In 1891 where I wrote Shuan? Pt Erin for Catherine Quirk widow - this must have been correctly "Struan".
It all fits together!