NSW BDM death registration (17250/1931) only records father's name as "Michaelis". Age is 75 (implying Year of birth 1856). Place of birth is Hanover Germany, with "73 years in NSW" (implying immigration in 1858).
No parents are listed on her marriage registration (2435/1880). Minnie records her surname as Michaelis.
The Vic BDM death index for Minnie's daughter Amelia lists her mother as "Wilhemina Johnston, maiden name Fraunfelder". This conflicts with the birth index listing mother as "Minnie Johnston formerly Michaelis 24 Hanover Germany".
One source suggests Wilhelmina's mother was Amelia J Fraunfelder (Nee Michaelis, b 1843). This Amelia would have been about 13, if Wilhelmina was born in 1856. This Amelia married in 1863.
Given the age difference between Amelia and Wilhelmina on Augustus' and Franziska's full death registrations, it is most likely they were sisters and the reference to Fraunfelder was a mistake when the death of Amelia (Wilhelmina's daughter) was recorded.
Michaelis, Wilhemina, 1856, CapeWill Tree on MyHeritage
For all the information I have on Wilhemina Johnston (Michaelis, 1856-1931) and her close family see my tree on MyHeritage that I am progressively transcribing. (B. Williams, 21Jan2019)