Which raises a remote possibility silly enough to be worthy of QC.
What if she wears a wig that's one of her father's inventions, using nanotechnology to synthesize continuously growing hair-like fiber out of dirt and dust, thus keeping it clean? There's not a lot of dirt and dust in Hannelore's environment, therefore it grows slowly, which explains why it's the same length it was before the Great Time Jump when the season changed to winter.