Hi Nicolas,
The leaves are a 'natural product', which you have used in an artificial way. If you are trying to simulate some sense of realism then you need to look at leaves, decide if you want to use them blown by a fan, say, or in a large heap that she has just leapt or fallen into, or maybe just a few on a marble floor or similar. The very first image, as the body is square with the frame, makes it look like its a forensic photo. The angle of the third one (the chin) is better. However, in the first, the hair colour blending with the leaves is 'of interest'.
I actually think, that just placing one leaf on each breast must be some sort of joke? It would work fine here if she was wearing a Kaftan, or a teeshirt, any sort of outdoor clothes, or a contradiction -pyjamas, evening gown, whatever.
I think I would try and think of some story line, build the set a bit more, get more leaves, (pine needles not recommended) maybe a wheel barrow and a rake, other props.
When she is looking out of the picture, I tend to wonder what she may be looking at, it reminds me too much of some 'pet' photography I've seen/taken... If there were more leaves, then the photo with her eyes shut (she looks asleep to me - its the first one she looks dead) would be fine. Or, just spread her hair, as in the first, and fade it into the leaves. It seems you have a good model, and you yourself are finding faults in what you do. Just play much more - go crazy.....
Just my opinion, hope it stirs something.
Best wishes,
Ray