I dont mind the arm in the first one- nice wide angle effect. It pushed the perspective towards the subject. I find the detail on the railing against the dark sweater to be distracting more than the arm. I end up staring at it instead of her :shock: !!
The second has an over done feel. There is no excitement or flare to it. No offense but it looks like a Guess Jeans ad from the mid 90's.
The third, I like. The colors are very graphic. Her head could be positioned a bit better - it almost looks kind of heavy and she's struggling to keep it up. maybe try it on a greater slope.
The forth is okay. Her position is good. It seems a bit dark though because I loose her shape int eh background and she appears as a head, hands and legs. maybe tweek the colors in PS and see what happens.
Over all pretty good for your first model shoot.