I shoot a lot of beach stuff so heres what I think:
1. Good job on the lighting. I HATE shadows so either you shot it with cloud cover or used a fill flash. Either way that's nicely done
2. Girls NEVER know what to do with their hands so the sometimes do bizarre things with them. In this case they aren't badly placed but... see how shes putting some weight on them? Then notice her tricep. Its bulging a little bit. Keep it feminine and weight on the feet. (Unless you're shooting a fitness model)
3. A little arch in the back would accent the chest and tuck the belly. (I know its not a bikini shot so the point is negligible, but an option to think about)