I had the same problem with my DD and this method worked like a charm...
Have your daughter start at the top of a slightly sloped area. Have her coast down the slope with her feet not on the pedals, but down near the ground, raised just high enough to allow the bike to move without her feet stopping it. This will help her with the balance part, which seems to be what she needs. Have her do this over and over until she feels comfortable and able to balanc. Then, when she has the hang of the balance part, have her start to do it while pedaling.
For my DD it was important to separate the two parts (balance and pedaling) because she just couldn't manage them together at first. Now she rides very well and has no problems.
Good luck!