Hi James, my question is what is the objective? Is it a first for the model or a first for you, or both?
Is it to show her as pretty or as a marketable commerical fashion model? In my opinion I can't give you meaningful feedback unless I know what your intention is with these shots because I am sure you don't want patronising remarks like 'well lit or well exposed' or even worse ' they are sharp'.
As generic model shots the second two show her engaging the camera. The second is a pose more suited to potential glamour although nothing indicates that glamour is the intention and the third one shows that she could actually sell what she is wearing, although she is standing awkwardly and it is off-kilter.
The top one looks like a family snapshot of your sister. That's not a criticism, but its also not an effective model shot in my opinion. It is neither a classic beauty shot, nor a fashion shot, nor a glamour shot. Sorry to sound harsh, but I am not only trying to help you but it is helping me by asking such questions and clarifying my intent when taking a picture
So it comes back to the first question I asked which you must ask yourself. What are the objectives of these shots? What are you trying to communicate and to whom?
Hope that helps
cheers
Nigel
(By the way, I am open to equally objective and realistic criticsm of any shot I post)