Yeah, as early work is more closer to that. I've seen her presented as participant of both movements, like many related young German authors of that era were considered part of 'Jugendstil' on a first stage as a step or initiation towards later Expressionism, that was in turn a global definition to encapsulate the diversity of intellectual currents based on the individuality, at least by German interpretation of it.More resemblant of Art Nouveau, though it's pretty close!
Searching now I have seen, as one of the first results, a very recent documental titled Lotte Reiniger - Dance of the shadows (Lotte Reiniger - Tanz der Schatten) that mentions her work as something pretty unique:
http://www.itfs.de/start/programme/rahmenprogramm/fokus-silhouettenfilm/19. International Festival of Animated Film Stuttgart 2012 - Focus silhouette film said:She had invented a new kind of artistic film somewhere between the aestheticism of Jugendstil, expressionism and magical fairytales.