Nebraska keeps it vital records very restricted. Marriages have been on file at the county level since 1909 but they won't release a copy unless it's your, your spouse, your parents or your legal representative requesting the copy.
That's why you don't find many of those records online.
I looked in the Fillmore County Marriages, www.rootsweb.ancestry.com/~nefill/mo/schools.htm
but her marriage wasn't in that list.
Marriages were recorded in Oklahoma starting in 1890 and are kept at the County Court Clerk where the marriage license was issued. Successful Searching!