Not a bad start! Some thoughts, though:
#1: Her face could use some more light. Either a flash bounced off of something or a reflector could help this one.
#2: I agree. This is the best of the bunch. Nice shot.
#3: This may be a personal thing, but when I see someone looking to the right, I like to see more image to the right. So I think this one would have been better with her on the left and more image to the right.
#4: I can't pick out what bugs me about this shot. It just doesn't look natural. Wish I could pinpoint what it was...
Hope to see more!
*EDIT*
I really liked #3 and couldn't let it go. Here's what I would have done in post processing:
-Cropped to remove dead left space, since she's looking right
-Added contrast to bring out the shadows and highlights of the tree and her eyes
-Removed color since I interpret her expression as somewhat somber, like she's reliving an unpleasant memory.