Just to say that during my childhood I heard both terms used, although
I can't remember whether there was a difference in application.
Also, in the dim recesses of my memory there appears a book
called 'Ochotniczka Helenka'. Perhaps a Pestka or Ochotniczka might
have some more information about this. Maybe the Veritas Bookshop
(Ksiegarnia Veritas) in London, England might shed some light on this.
They have books in Polish and English dealing with history, memoirs,
Polish music on tape and CD.