Many thanks for your help, this pretty much solves the mystery. My great great grandmother Emma Light died in 1869 at 32 Princes Street. The informant, present at death, was “Mr A. Relihan of 3, Green Street. I have not located a Mr A. Relihan anywhere. However, John Relihan lived at 3, Green Street in 1871, whose wife was Emma’s sister in law. It now seems obvious, looking at the map, that Emma was almost certainly on a family visit when she died. She was 38 when she died of “morbus cordis” (heart disease, so maybe sudden death). Her youngest child was under 2.
I don’t know whether the rest of her family was with her at the time she died. She was buried back in West Ham, so no reason to suspect a family rift. Princes Street seems to contain quite a lot of lodgers in the census, so maybe she was in a sort of b and b. I also wonder whether Mr A. Relihan might simply be the result of the mis-hearing of John Relihan saying “J” and not “A”?
Dave