I'm sorry ahead of time - this is going to be a negative critique. Please don't take anything I say personally. Take it in the spirit it is offered - as one photographer to another and as a way to learn.
For the longest time, I could actually tell a digital image from a film image. To me, digital images always *looked* like video stills. They were cold and metallic and overly sharp. This one looks just like that.
Photographer means "light writer". We use light as our medium just as a sculptor uses clay or stone. If we're going to create appealing, or even good images, we must be aware and concious of the light. I can tell from this image that it was taken during mid-day in full sun - notoriously the worst time of day and the worst conditions to take outdoor natural light images. The colors are washed out - the contrast is high. The highlights on the water are very specular. The shadows are deep.
That is not to say that you can't produce good images under those conditions, but it is difficult. It isn't light that is important - it is the quality of the light that is important.
How could this image have been improved? There are posing issues, but I'm not fully versed in the nuances of posing, so I'll leave that to others. As far as light color, however -- you could have shot this early in the morning or later in the day when the sun is low on the horizon. The quality of light at those times of day is much more appealing. It is warm; colors are brighter; shadows are more even. You could have shot this at noon outside with cloud cover, like a giant softbox. You could have shot this under the cover of a picnic area, or with an umbrella or scrim over her to filter the sun. You could have shot this in the shade. You could have shot this with a soft gold reflector bouncing light back onto the shadow areas.
And, you could have shot this with film, or at least with a digital camera that doesn't give that tell-tale "coldness" so many digitals do.
Hopefully Kyna is a girl you can work with again. Try to shoot later in the day, or at the very least, not in the full bright mid-day sun.
My firstish shot with my new D70 - 7pm, outside my front door.