no idea, there is just one. I dont think this is her actual "origin story" though if she even has anything concrete.
Groke (or Mörkö in finnish) is somewhat mysterious entity. She either hates warmth or craves it terribly and either way will freeze everything, can't say which.
In the cartoon/anime she just appears one day, looking for a thing that was taken from her. Moomins had never heard of her before. Also, in the cartoon/anime she is absolutely terrifying, like nightmares for years grade terrifying for kids.