In general, I agree that "hasta siempre" means that you don't want exactly to say farewell, but you might not see that person ever again.
Btw., Ché Guevara made famous "Hasta la victoria siempre" (which would mean something like we'll keep on fighting until we win). Maybe her use of "hasta siempre" is a personal interpretation...
But before I keep weaving more strange thoughts, let us know when she explains, will you?
