#1: I feel like there's sooo much of the environment and so little of her. I would crop the right off and make it a little closer. Her left arm is a little blown.
#2: Same thing as #1 and the blown out vanishing point with the saturated-out-of-it's-ass---bush is really distracting! I also don't like the
way her arms are crossed, because although her face is relaxed, the body language isn't and throws the photo off for me. It gets really blue from her legs down, especially the sidewalk. Aside from these, the exposure is quite nice.
#3: A good shot, but it's super posy. Why is her arm up like that? It seems really stiff and unnatural. I think it would've been better if it was higher over her head, it just seems awkward the way it's just a right angle there. I'm not feeling the shadows on her arm either.
#4: I like the symmetry of the flower bushes, but she's totally blown. Look at the highlights on her arm and face and wrist. Extremely white and no detail. This pose is the classic senior portrait pose..classic or cliche, you decide. I would have liked a bit more light to catch in her eyes (for all, actually!)
**I don't know if you incorporated more of her ballet outfit or what not, but surely you could have played on it more within the environment or another one. Maybe her in a ballet stance or something with her and her pointe shoes.
**I know this is your first Senior Portrait shoot, but is it also your first portraiture?
Either way, I think you've got the right idea and they came out good with some common flaws that can be learned from and prevented next time.