If the mother died, or the father, but more commonly the mother, then the youngest baby sometimes was raised by relatives or someone else that could care for her.

The thing to do would be to try to find a Vik family in Grant county who could have the baby Mabel. Vik also has the spelling variations of Vig and Wik and Wig - in Norwegian, which is the origin of the name. It is a farm somewhere in Norway, which is by the ocean, with a bay or place to land a boat. That is what Vik means.

The 1900 census says that she is born in Dakota, on March 1894.
It also says her father is from Norway and her mother is from Sweden.

The 1900 census shows that Peder N. Brevig has a father Nils N Brevig. (plus Mabel Vik living there)

https://familysearch.org/pal:/MM9.1.1/M9S8-34X

Possibly a relative - maybe the fact that Peder Brevig's parents are living there in 1900, perhaps it was a child of his brother? Grandparents have custody?

Maybe an obit for the grandparents would tell something too.