My search tip would be premature in your case, because you lack the birth surname of the adoptee, your mother. But if you acquire the surname in the future, be advised that North Dakota is said to have conducted a state census in 1925---and you could look up people using that surname in the birthplace.
That information is from a book titled, "The Source: A Guidebook of American Genealogy."
Reg Niles
P.S. If the adoptee applied for a Social Security card, you might want to obtain a copy of the SS-5 form she filled out at that time, to see what she listed as names of parents. I do not know exactly how to apply for the copy if the cardholder is living. If deceased, find her entry (if any) on the online Social Security Death Index
http://ssdi.rootsweb.comthen click on "SS-5 Letter" on the right hand side of her entry. There is a fee of $27 to be paid to the Social Security Administration, and it may take months to get a response.
Not everyone is on the SSDI. It is mainly for post-1962 deaths that were reported by local officials or funeral directors to the Social Security Administration.