Please figure out how to post larger right here on GG. I hate having to go somewhere else to see the image and come back here to critique. But I love Stephanie to death and so I'll give you my input on this image.
First, there's really nothing Si about this image. When's the last time you say an SI Swimsuit issue? The background is a little distracting above her left shoulder. Since she is posed so the line in her body goes from bottom left of fram to top right, I am drawn to a spot that already has issue even more. The shirt? So SI model wears shirts anymore. Get her in a top that matches her bottoms at the very least.
Eyes are way too dark. They look like wholes in her head. Use that sand (giant reflector BTW) to bounce some light back up into her eye sockets. Instead of having her lean back and lower her head, have her lean forward just a little to allow the light to get past her breasts. That'll help with the chin to BTW.
What's up with that shadow coming across her abdomen right above her right hand? It's like she's cut in half. Put her hair on the other side of her head to open it up to some light. Way too dark in the face overall. Right leg is casting a shadow over the left that seperates her foot from her loer leg. Bad. Have her move her left leg forward and slide the foot into the right so the foot is in shadow at the very least.
On a good note, you filled the frame with the model. That's a step in the right direction.
Now, go forth and practice!