Lose the Training Wheels now requires riders with Down syndrome to be at least 11 years old. I have to say I agree with them. Their success rate has increased dramatically since they started the age requirement. I know several kids who are younger who are successful independent bike riders, but they are a small minority.
If you child is too big for a bike with training wheels, you might want to look at Fat Wheels. They turn any bike into a "quad" bike and are much cheaper than a Trike.
Hannah will need to practice every day for a while before she is a completely independent rider. She needs to be more aware of her surroundings, get better with steering, touch up her balance, and learn to use her brakes more "gently". Our goals for Hannah were for her to have fun and gain skills. Those were accomplished, plus she only has some polishing up before she'll be hitting the bike trails!