Take this as just what it is, thoughts of another newbie to digital.
The first photo of her with her guitar I would have taken portrait orientation, or cropped tall instead of wide. The second one with her and her guitar I would have cropped a little closer with a little better better composition (rule of thirds). Also, that large tree directly behind her head bothers me a little too.
The one with her petting the horse, much closer crop and probably a taller crop instead of wide. I personally don't want to see more of the horses body than its eyes and face and maybe a shoulder. The horse takes up more of the photo than that of the subject (the girl) and, to me, that detracts focus from the girl.
The one with her sitting at the tracks is good but, again, I would have included more sky and less foreground I think. Maybe taken from a different angle and show the tracks trailing off in blurred bokeh.