Good job for your first set! I agree that 4 and 5 are my favorites. I might have cropped 4 a little differently...moved her more off center, to a better rule-of-thirds location, and either cropped out some of the sky or added some blue to it in post (as it is, that much grey/white is trying to pull my eye away from her).
I personally like number three. Yes, she clearly looks rigid, not relaxed like in 4 and 5, but I wouldn't call it awkward. This is a great pose for an athlete (back straight, head up, shoulders back, focused expression). I'm not at all surprised she likes it. I also like the foliage where it is. Between the lines of her body and the foliage taking up that corner, the whole shot has a nice diagonal flow to it, from lower left to upper right. The image would be more stark and boring if the entire background were rock. The only nitpick I have about #3 is the softball glove on its side at her feet - it took me a couple views of the shot to even notice it. Not that I have any better suggestions (there's a reason I don't generally use props), but making it a little more visible would have added to the shot and made it more clear that she is a softball player. Perhaps using a softball to prop it up on a nearby rock (think a mini still life setup)?