Have you looked at ship passenger lists of her coming to England. You would get her and husbands name.
I wasn't perhaps entirely clear. We don't know what her married name was and who her husband was.
As above
Mary Hodgman Tyree b 1872 Queenstown NZ
Has a birth record
Known as Polly which was diminutive of Mary or Mary Ann
Last known whereabouts Nelson, South Island, NZ in 1892
She had portraits taken at Tyree Studios by her brothers at this time
Married unknown man no record ever found
Traveled to London from origin unknown
Drowned with him in some kind of accident
Occurred in the Thames River
It would have happened after 1892, speculating in the 1890s
She is never mentioned again even in wills and probates
Which now brings me to this speculation. If Polly was never mentioned in wills and probates, and her mother died 1895 and her father 1899, it means she was deceased by then. So it is likely the accident happened between 1893 and 1894. Traveling overseas (if it wasn't a domestic trip) was often reserved for newly-wed couples.