Apparently you are not a descendant of Carrie and Peter Nordin - so perhaps you are connected to the Wallins.
Will you please say where the Wallins come from, who are their parents, where did they live prior to their appearance in the census with Carrie and Peter? That could be a clue to the whereabouts of Carrie and Peter in 1900.
Actually maybe you know where Carrie and Peter are in 1900? You didn't respond to my earlier question about that; maybe you didn't notice the question...?
A family tree online suggests that the Anna Aasland buried in Valley City, Barnes, North Dakota is Anna Serine Selsand and that she was born in 1901 in Ransom County, North Dakota. So that's a birth record you'll want to obtain via the county, if we can't find it online. It will state the parents of this particular Anna (according to the family tree online, anyway, which we don't know if it's correct or if it's the sister of your Carrie).
Billion Graves record gives exact day-month-year of birth plus middle initial (for future reference these are key details that you would want to include in your opening statement):
Name: Anna S Aasland
Birth Date: 15 Apr 1901
Age at Death: 91
Death Date: 1 Aug 1992
Cemetery: Memory Gardens Cemetery
Burial Place: Valley City, Barnes, North Dakota, United States
If Carrie had a sister born in North Dakota, then Carrie had a parent or a step-parent who immigrated to North Dakota.
Your opening statement says re. the surname Aasland that you "also see it spelled Assland." Where specifically did you see the name spelled Assland? As far as I can tell so far Albert is Albert Edwin Aasland and his father is Jorgen Aasland and mother Sophia Moen and he was born in Day County, South Dakota and he died in 1982 (so his obit would tell more, also his death record) - but I haven't thoroughly checked that, as this may be stuff you have already researched? (that "Assland" comment makes it seem you've looked into records)
FYI I have looked for Carrie's immigration and so far no luck.
Okay, that's it. Thanks!
BACK IN AN EDIT
US Public Records Index (Ancestry.com database)
Name: Albert E Aasland
Address: 725 5th St SW Stsw, Valley City, ND, 58072-3715
This address matches Carrie's death certificate - so this is definitely the right Aasland family.