Actually, Mary, it is not too early to tag her as "unknown" since that is her current status as far as your research is concerned. And if/when you finally determine her correct LNAB, you will be able to correct it on her profile.
What happens when we change the LNAB is that a new profile is created, and the old profile simply redirects to the new profile. Over time and thousands (millions?) of changes, we end up with a lot of server strain (redirect tangle, perhaps?) that we could avoid if we wait until we have more information.
However, we also currently have a ready source of reusable profiles that we can use to connect individuals with unknown LNAB if we feel a profile must be added to fill a gap in a section of the WikiTree to enable us to continue our research on the related profiles.
So go ahead and recycle one (or more) of the Unknowns, leaving the current LNAB as Unknown/UNKNOWN (or other variation). Then continue your research and maybe someday you can change the profile from Unknown to her correct LNAB!
And if I've THOROUGHLY confused you, let me know!!