Actually the centre of gravity is pretty low and towards the back because almost all of its weight is coming from the rider who is sitting above the rear wheel. It's misleading, I admit, because of the odd shape. The steering isn't different as far as I can imagine; it's the direction the wheel rotates in, not how big it is.
And yeah, the seat's a little too high for her but not by much. Depends if that's her actual crotch or just the bagginess of her shorts. When seated on the saddle with a foot on the pedal, the ideal height is such that your leg is almost straight, but not quite. I think what would actually be a problem is it would have a low top speed due to the small wheels (but then a faster acceleration perhaps) but I don't know how much gears can overcome that.
