It may be unimaginative, but I don't think that Magda was necessarily related to Julia or Natalie. I never really felt that there had to be any sort of connection among characters who simply looked alike. For instance, I don't believe that Willie is a lost Collins or that Sandor and Count Petofi are related to the Stokes family. It can be fun to speculate, but those theories can often become very complicated.
ProfStokes