Hello, Wendy!
If you need a profile for someone (in this case, a spouse) whose LNAB (last name at birth) is currently not known, try recycling one of the profiles from the Recycle Unknowns category:
http://www.wikitree.com/wiki/Category:Recycle_Unknowns
Just adopt one of these profiles and add any info you have for the spouse to the profile (you may have to delete some old info). When you eventually discover the LNAB, you can edit the profile from an Unknown to the correct name!