I topped after the third node, but that was designed. I wanted to use a lot of LST, so I needed a few branches to train. I've read where people topped after 1 node, or even up to 5. The only thing I would consider is the health of the plant. If she is growing vigorously, feel free to top her, but if her growth is slow. or there are deficiencies, take care of those problems first. Topping is stressful, so make sure your girl is healthy and can handle to the stress.