Ouch! My sympathies on the cracked rib. I hope you're feeling better!
Photoshop is a useful tool, but I recommend building strong composition skills first. This will save you many hours of frustration. I see you have Picasa, which is not a bad program to start with for basic photo editing.
In general, try moving closer to your subject. She's getting lost among all the foliage. Use a narrower depth of field to pull the focus onto her and blur the woods.
Be aware of your available light. Though there's a good deal of ambient, she looks very dark. This can be solved by using an off-camera flash or by moving her into lighter areas.
A very pretty setting, perfect for an Earth Kingdom warrior! I like the water reflection. The rocks create a strong vertical line, and having them tilt makes me feel like she's about to fall off! You need to straighten this shot. Also, you can crop in closer without losing the nice reflection.
Crop in closer. Adjust your lens so the focus is on the cosplayer and not all the trees. She should be sharp, but we don't need to see every leaf and twig.
You caught some great light here! The deep shadows and back lighting makes her look intimidating. Try having her glare right into the camera, and again, move closer or zoom in! (Not crazy about you adding another person into the edited photo. He was obviously shot at a different angle than Suki, so he does not fit in at all. However, I DO like the closer crop! A good start!)
Needs to be straightened. The tilt fights with the straight line of the fallen tree and the lake. (In the edited photo, blurring the background was a good idea but the selection is very messy and distracting. There's a straight line at her feet across the grass, and real grass simply does not behave that way.)
You've made a good start by shooting your subject in an interesting location. Keep practicing, I look forward to seeing more of your work. Thanks for sharing your shots!