Cute girl and nice captures. As I was looking, I was 'noticing' the use off the off-cam lighting quite a bit - in particular on #'s 4, 5, 9 and 10. When you look at number 5, it looks very flashed because the trees in front of her are well lit and it is very dark behind. I think if you expose that shot for the ambient, and then give it a little kick with the light, it would be much more natural looking. Same for number 1.
I think as you experiment with outdoor lighting, you will find that you can get the extra kick you need without the light being so noticable. It's a tough balance, and I am working on finding the right balance myself, but each time I shoot I get happier with the results.
I too prefer natural light, but there are times when there just isn't enough of it to get the pop you want in a portrait. I've been using a wireless flash in shoot-through umbrella mounted on a monopod that my assistant holds at various locations and angles.
