I did a bit of a timeline as I see it pertains directly to Agnes' whereabouts ... and it raises one question, and a location:
1879 Agnes and William married in Christchurch
1879 - 1890 Agnes and William moved to Wairoa
1880-1881 Agnes was unwell in Tauranga (and Auckland somewhere between Wairoa and Napier) (ER entry for William)
1879 - 1890 Agnes took off to Napier, William followed
1890 Agnes went to Christchurch to seek work
1890 - 91 Agnes was paid passage back to Napier
1890 - 91 Agnes was paid passage back to Wellington
1891 October 19 Maintenance set at 30s in favour of Agnes from William. Wellington.
NOTE it says 4 little children.https://paperspast.natlib.govt.nz/newspapers/EP18910704.2.8?query=agnes%20fulbrook1892 Margaret born 29/10/1892 (BDMH)
1892 November 7 William wants custody of the children. Napier
https://paperspast.natlib.govt.nz/newspapers/DTN18921107.2.8?query=fullbrook[Divorce article states he had not cohabited with her since her departure to Christchurch].
1895 Agnes applied for maintenance from William to be increased
1896 Agnes and William divorce, at William's initiation
1896 Agnes Patton Fullbrook 1896 Napier Hawke's Bay (electoral roll)
1896 James Stevenson, Waiter, Masterton (as per divorce article)
1900 Agnes Patton Fullbrook 1900 Napier Hawke's Bay (electoral roll)
1905 Agnes Patton Fullbrook 1905-1906 Christchurch North Canterbury (electoral roll)
1911 Agnes Patton Fullbrook 1911 Wellington Central Wellington (electoral roll)
1912 Agnes Wellington to Sydney
1913 Agnes Electoral roll in Sydney
1914 Agnes Patton Fullbrook 1914 Wellington North Wellington (electoral roll)
1919 Agnes Patton Fullbrook 1919 Napier Hawke's Bay (electoral roll)
1921 Agnes Auckland to Sydney
1924 Agnes idle and disorderly, Wellington
1924 Agnes Wellington to Sydney
1925 Agnes died in Sydney, Australia
So, the question:Maintenance in October 1891 was applied for by Agnes from William. The newspaper article states 4 little children. Margaret according to BDMH hadn't been born by then.
Is there another child? When William showed up to the maintenance hearing in November did he know or not know about Margaret?
Births to Agnes1880/2942 Fullbrook Stephen Round Agnes Patton William Wood
1881/16203 Fullbrook Richard Outen Agnes Patton William Wood
1885/5662 Fullbrook Agnes Anne Matraners Agnes Patton William Wood
1892/12976 Fullbrook Margaret Howard Moore Agnes Patton NR
The location:It would appear that Agnes was living in
Wellington when Margaret was conceived and born.