I like this work. The shading is clear, and from the front angle, allowing you to see the musculature all along her body, and her use of bending is very creative to give her a dynamic pose, as well as an excuse to look confident (whereas I find it usually looks a bit...silly when they look cocky and confident standing completely still.)
My biggest issue is the hair, which looks like it sits way too high and is far too voluminous for Korra. It looks more like a wig. Also, while there is no clear motion anywhere else in the picture, her breasts seem to be bouncing as if she were falling. Some indication of movement (water curling as if it were dropping, which would also add a nice dynamic that looked like Korra was bending the water constantly, rather than just a single pillar with ease).
The calves, forearms, and shoulders are well-defined but rather small. Korra, even in the show, had a very broad, muscular back. Although showing her front, her shoulders still need to "pop" a bit more.
Another issue is the trim of the bikini. The pointed areas don't seem to have any purpose, and I find they are more aesthetically distracting than pleasing.
And, finally, the face is a bit too..."soft"? Child-like, I suppose is a good way to put it. Korra has very stern, but not masculine, features. She is young, but she is a (mostly) grown woman, this picture looks too much like the face of Korra as a young child.
All in all, a very solid and well-crafted picture, with room for some improvement. Overall, I'd say a 4 to 4.5 out of 5 seems fair.