Update! Istra insisted in going to to practice the bike again the day after the video (today), and by mid-afternoon she was riding entirely by herself. She still has a bit of trouble getting going, but she gets going eventually, and then goes pretty well... for her first day as a two-wheeler. She really likes using the drained wading pool in the park to help her get going. She rolls down towards the centre while getting her feet onto the pedals, and the pedals up the other side.