Go to Walmart and buy the cheapest kid bike (WITH a hand brake!) that fits her (or find one on CL or whatever) and remove the crank/pedals altogether . . . she'll have to push herself along with her feet and she'll learn to balance the bike better and before long will start finding herself keeping her feet off the ground for longer and longer coasting. And then she's got the balance down to a "T". Add a bike with pedals after that and it's a piece of cake.

I did that with both my kids and ended up giving that training "scooter" to a friend when he wanted to teach his daughter to ride. Worked quickly and like a charm.