Used Genesis 24" Blue Whirlwind Girl's Mountain Bike
I got for my wife, but then decided to go with a adult trike instead . We never used the shifter to change gears , they do seem to work ok though. it has street tread not knobby tires with slime tire sealant in both of them. 

21-speed drivetrain with Shimano rear derailleur

Easy-action twist shifters

Front disc and rear linear pull handbrakes

24" alloy wheels

Rise handlebars  

Overstuffed bumper suspension seat with quick-release seatpost clamp 

Standard pedals

Height suggestion 4'6" & Up

Ideal for tween/adult females