This second shot with the dart, is the one in which she is throwing it and the dart needs to remain still in the air. We already removed the dart, so we just need to merge the 3D dart over.
Dart Integration
I used the same integration as in the other shot, copying the script. Then, I added a framehold in order to be able to work with a still frame.
As the dart needs to do the movement from, her hand to the air, I added a transform note, and I followed the movement of the original dart until the place in which I want the dar to be.
Fnally, I added motion blur in order to make it look more realistic. 
And with this, the shot is ready to be exported for the final editing.
MA Visual Effects 