The K-2 non-immigrant visa allows a child of your Fiancee to enter into the U.S. and await the availability of an immigrant visa.
K-1 children may stay in the U.S. on K-2 visa for a maximum period of 90 days from the date of entry. If you and your Fiancee do not marry within 90 days, K-1 children must depart the U.S. together with your Fiancee.
Generally an interview is required at the American Consulate. Some consulates do not require a child of your Fiancee to attend if s/he is below the age of 14. Many consulates require a child to attend even if s/he is not going to move to the U.S. with K-1 parent immediately, but will follow later.
The cut-off date for issuance of a K2 visa is 1 year from the date of the K-1 visa issuance to the principal alien. K-1 and K-2 visas are valid for one entry into the U.S. at any time within the next six months.
The child of a K-1 principal alien may acquire K-2 status even after the principal alien has married American Citizen Petitioner and acquired lawful permanent resident status in U. S.
a. reside in the U.S. for 90 days until K-1's marriage;
b. study in the U.S.
c. apply for work authorization.