"Relation by marriage". Goddess ase.
Goddess and wife of Thorr, we do not know her own myth and her name ("Relation by marriage") would reinforce the banality of the character. However, to justify the skaldic kenning who calls gold "the hair of Sif", Snorri tells us that Loki, after having maliciously cut this hair, had to reconstitute it under the threat of Thorr, he would have entrusted this task to the "alves dark” (dôkknlfar) that are the dwarves. Loki takes the opportunity to have various marvelous items made at the same time, such as Odinn's spear and ring - Gungnir and Draupnir -, Freyr's boat and his gold-bristle boar - Skidbladnir and Gullinbursti - and the Thorr's hammer - Mjollnir.
If we only remember Thorr's aspect as the god of fertility, Sif's hair could represent the field of wheat waving in the wind.