Leni Riefenstahl's next cinematic work was very likely made specifically for Adolf Hitler himself. The film was financed by Hitler through the German government; it is a film version of Adolf Hitler's favorite opera: Tiefland by Eugen d'Albert.
Based on the great Catalan writer Àngel Guimerà's 1896 play Terra baixa; Eugen d'Albert's Tiefland was his seventh and most famous Opera; though not immediately popular, the opera would garner international acclaim shortly after it was reworked by d'Albert in 1907.
Tiefland would be Leni Riefenstahl's last full length feature film. Once again she would direct, write, star, edit, and produce the film. I've seen the film and it is a very high quality work, it's a very artistic film and I feel that Leni Riefenstahl's vision is well supported, especially taking into consideration that the film was created during such a hectic time in her life, and of course a very hectic time for the entire world.
While Tiefland is not quite as much of a breakthrough as Leni Riefenstahl's great work done in Triumph of the Will and Olympia; Tiefland is full of extremely high quality, beautiful shots, and I believe it to be a fine film overall.
The one draining issue with Tiefland is that some of the actors were taken out of concentration camps and put to work on the film. Both Sinti and Roma gypsies were taken from concentration camps nearby wherever the shooting location was at the time.
It's said that the actors in the film were later put to death at some point after returning to the concentration camps. Whether that is true is unknown to me, but it seems that it was likely unknown to Leni Riefenstahl if it were true, as she denied anything like that ever happening. Regardless of the fact that many of the actors in the film were gypsies, or whether they were being forced into doing the work or not, or whether they were killed by the Nazi's at some point after the filming was finished; we have to realize that it was a terrible situation for them, as well as many other people during World War II, but it is a fact of Germany from that period in time, one that we have to accept and deal with.
It's unknown to me how Leni Riefenstahl treated her actors, but I can't see it as having been too bad, certainly not as bad as what was happening to them inside of their concentration camps; taking into account the fact that she was acting right there along with them. Who can say how they were treated while in her presence and working with her though.