Now, since she's 5' even I think you'll be hard pressed to find a light MTB that'll fit her even with a 60mm stem and compact bars. Maybe if she has a long torso and long arms...

In 1988 Giant made bikes with extremely short ETT but this one was about 29 lbs. The Iguana was entry level so maybe they made a lighter one with same geo but I dunno. It even has everyone's favorite road bike feature - toe overlap!