The very friendly lady of the archives where the registers of Loosdrecht are kept just got back to me. There is no trace of Johanna Margaretha or her mother and sister in Loosdrecht. She searched various registers (population, domestic servants, incoming and outgoing persons) but unfortunately nothing.....
There is only one thing we can still do, and it is a long shot.
Instead of searching forwards in time, we can search backwards.
In 1886 mum Margaretha van den Berg and sister Johanna Maria Stuffers registered back in Haarlem, coming from Vreeland. "Our" Johanna Margaretha is already 2 years in the USA by then.
But.... The 3 ladies left Haarlem together, and after Johanna Margaretha left for the USA, the 2 remaining ladies came back to Haarlem together. Is it possible that the 3 of them stayed together untill the departure of Johanna Margaretha? And could they have lived in Vreeland all those years, instead of in Loosdrecht?
I sent an email to the archive where the registers of Vreeland are kept (Regionaal Historisch Centrum Vecht en Venen), explaining what we are looking for.
They may have the answer, and even if mum and sis came to live in Vreeland after Johanna M left to the USA, they can tell us where they came from. And then we have another starting point to continue our search.
It was (and still is) obligatory to be registered in the register of inhabitants (population register), so we may get some results, fingers crossed.....