Ann,
I did not find out much about Nadezda, except that she was from Orenburg. She could have been a descendt from Danish - as per her name. Catherine the Great brough Germans/Europeans to populate that area, as did GD Nicholas K (the angry steps). So it is very possible that she could have been Danish.
Amelia
(Eva McDonald)
Nadezhda Dreyer's father, Chief of Police in Orenburg, was called Alexander Gustavovich (von) Dreyer and her mother Sophia Ivanovna Opanovskaya, according to the Russian Wikipedia. From
this database of foreigners in pre-Revolutionary Russia we see that her father was a Baltic German.
This is her grandfather Gustav von Dreyer, apparantly an auditor and estate owner in the Narva area.
The name of the estate, Slepow Koniec, seems elusive, though. It's probably not in Estonia, as it doesn't sound like (Germanized or Russified) Estonian at all. In Russian Слепов конец means something like End of the Blind.
BTW Dreyer is a not uncommon name in both Scandinavia and in Low German-speaking areas and means "turner".