Put a small rack on the back of her bike - I remember when I was little my Mom bought me and my older sister identical full-size bikes. My sister was taller and learned to ride hers first. But I was too short for mine so I would run alongside it and try and keep up with my peddling sister. My Mom threatened to sell my bike if I did not learn to ride it. My neighbor saw me running with this obviously too tall bike and offered my brother her granddaughters bike to use to teach me. It was the perfect height and it had a rack on the rear. My brother put me on the bike and coached me to pedal while he was holding the bike upright with his hand on the rack. We went around the driveway several times and I was peddling like crazy while trotted along behind helping me balance. He then let go of the rack and I was balancing and riding on my own. I have seen a product at Walmart that consists of a large u-shaped handle and it bolts onto the rear of the bike - that looks like it would work the same way that rear rack did. Good luck and be patient. My Mom wasn’t with me, but thank goodness my brother was. She will be riding along with you in no time.
“No Bird Soars Too High If He Soars With His Own Wings” ~ William Blake