Geoff650R wrote:CRF50's are 1 speeds and use a torque converter i think.
Dudes and dudettes: Z50's, XR50's, CRF50's, and most XR/CRF70's all use a 3 speed auto CLUTCH MANUAL SHIFT transmission. No Honda has a auto transmission (bikes - we're not talking about atv's here).
Anything with an auto clutch and a traditional gear box uses 2 clutches. One is activated by the motor revving up and centrifically throwing clutch shoes against a outer hub that looks kind of like a brake drum on a car. The other is very similar to a manual clutch but the push rod for the deactivation is connected to the foot shifter instead of the cable to the handlebar.
To the original author's question, if you don't mind hondas look for a CRF230F or a CRF150F. if you're buying new Make sure you specify the F model on the 150 because they make a new hard core 150 racer. That would be fun, but then she would need to learn to use a clutch.
You will need to take her to a open field and teach her how to go through the gears on any of the auto clutch models. If she's been riding the trail boss and liking it then with proper encouragement she should catch on.