Agree that finding a well-fitting bike, then "electrifying" it is a good idea. One other consideration that was helpful for my daughter (albeit at a much younger age) was to have her on a "half-bike" (or whatever they're called) that was attached to the seatpost of my bike. We rode blissfully together off road for about a year like that, then she started on a two-wheeler. Sounds a little crazy, but might give your daughter the stability and confidence she needs.