I suspect British Possession did mean IoM and that she lived in Douglas (there were many boats to Liverpool each day during the holiday season then) and the child was fostered on Island.
- the July departure of future husband to Sept marriage is only just enough time for voyage - were they on the same boat?
I have a brief collection of published letters from 1904 and it took 7 weeks from Liverpool via Capetown to Melbourne (it would take a further 2 days to Sydney) - maybe less if via Suez but think most passenger ships went round the Cape as South Africa was a major destination