If bitd goes to the 80's, there were a few options, many of which included 24" wheels in the rear or both front and rear. My ex-wife was about 5' tall, and I built up a few 80's bike for her- a pink 1987 Cannondale with 24 inchers in the front and rear (aluminum); a specialized stumpjumper, again with 24" wheels front and rear (steel).
Then there was the 1997 Independent Fabrication's "Special" (Steel of course), that was made with "female specific" geometry and a seriously sloping top tube, to the point that it looked like one with the seat stays; it had 26" spinergy wheels, and complete xtr m950 components. Loved that bike; it was a 10" frame, or something like that. Have pics of all of these; can post later.
Like nate states above, Fat City Cycles had small offerings, which continued with IF. Also, Kona has some very small sizes, as did Specialized. For a 90's MTB, you have many options, but getting a small 80's MTB is more fun, while being a bit more difficult.
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