Do know that as good as everything we know of Norse mythology comes from writers after the Christianization of Scandinavia so I can't write about any older myths (this might be my shortcoming since there are definitely users on this site with a much greater knowledge on this subject than myself).
The only connection Sif would have to warrior culture would be her marriage to the storm god Thor.
In a Dictionary of Northern Mythology the author noted that Sif's name was
Her name seems to mean “relation by marriage,” so even here we find nothing of
a personality or function – just a familial association.
Sif’s association with
the vegetation on the surface of the Earth, which is suggested by the nature of her
hair, is also corroborated by the fact that a species of moss
(Polytrichum aureum) was called haddr Sifjar (“Sif’s hair”) in Old
Dictionary of Northern Mythology Rudolf Simek
D.S. Brewer, 1996 quote taken from Norse Mythology for Smart People: Sif
I think Sif's warrior like looks and behaviour in the movies is ofcourse greatly exaggerated in the name of entertainment. And rightly so since I enjoyed the extra take of her being a beautiful strong weapon wielding woman. But as most cinematic versions of any mythology or history they are mostly incorrect and use some "artistic liberties" to make the plot more available and titillating to a broader audience.