Susannah TATCHELL died in 1897 as the age of 63 so I can’t see there was a need for a nanny in the early 1890s when Margaretta was not much more than a child herself.
In fact the TATCHELLS married at Willunga in 1851 and no children were recorded for them at all in SA and I cannot imagine them having young children 30-40 years later that needed a Nanny.
Does the SWEENEY/ALLINGHAME researcher have their details correct with the following? Since others have been confused so their research be might also be confused.
"6 iii. William James Jones. . . .. He married Margaretta Bowen-Tatchell in Finnis, South Australia, 27 June 1895. Margaretta was born 1878. Margaretta was the daughter of William Neal Tatchell and Susanah Arrington"
Margaretta's age was recorded as 20 at the time of her marriage in 1895, then her age was recorded as 82 when she died in 1957 so her birth year was more like 1875. But then registration details are actually known to have mistakes even though it appears the recorded marriage and death ages correspond.
Unfortunately there are just too many inconsistent details to know for certain what is true or not.