I'm getting vibes of Nordic Huldra or Rå (which would essentially map to Nymphs in Glorantha) but less malicious. She turns up in myths a fair amount as the mother of various less-civilized offspring (Odayla, Ormalaya, Ironhoof's son), so perhaps it's not so much that she can't be caught, as that it has to be a proper hunting/courting combination? She also at times seems like a counterpoint to Ernalda, being the wild lands instead of the cultivated ones. Beast absolutely seems right for runes, and I do agree that it's hard to pinpoint her as either theistic or spirit.