Search teaching a kid/child to ride on this section - umpteen threads on it.
1. Remove pedals (LH pedal has LH thread, i.e. opposite to normal
2. Make sure she can reach ground easily with feet but legs not very bent
3a) find gentle slope, preferably leading to level ground, and get her to roll down it until she can keep her feet off the floor for a decent distance
3b) If no slope, get her to "walk" the bike along until the same thing happens
4. When she can travel at sufficient speed to keep her feet of the ground and steer reasonably well, put the pedals back on and then your troubles start.
5. Once she can ride, she may need a helping hand to get going until her muscles become strong/co-ordinated enough. If so, place your hand on her back, don't push the bike - it will then go where you're pushing it, which may not quite be where she's steering it.
By the way, there are some very good tips to be garnered from a BBC East Midlands programme which is on their website, where an adult reporter is taught to ride on line - I'll try and find it (in fact it's on this forum under the heading "Kylielearns to ride and then takes a trip". The teaching is a model of clarity and structure.