Haley - No real reason not to run.
Fallin - Never really had a niche, never seemed interested.
Martinez - Not ambitious, mostly talked about because how good she would be as a candidate.
Ayotte - Hasn't done much, has never really sought national attention.
Rice - Time has passed, never seem interested in running for anything.
McMorris-Rodgers - Not well-known, no real niche, from a state that's irrelevant to GOP politically.
Blackburn - lolwut
Fiorna's probably the only GOP woman in the race. At least until she drops out shortly before or after the Iowa Caucus.
Fallin's niche would seem to be the really hard-edged social conservatives, given her "cut off all soldiers' benefits to make sure gay soldiers don't get them" stance. Cruz basically boxes her out of that niche, though.