I don't know if you cropped your shots the way they are, or if they were taken that way and simply resized.
For the second one, while I agree it is a nice shot, and again I don't know if you took the shot the way it is posted, or if you cropped it so that there is less in the direction the dog is looking, but I probably would have done it the other way around. The space on the other side of the dog appears to me to be dead space and would've kind of made more sense on the other side of the dog. But that is just MY opinion. Again, it's a good shot.
Four is probably my favorite. But I agree, I would crop more off the top, probably from the door frame and up, making sure to leave the toy in the background. Again. Just my personal opinion.
The last shot, I would have cropped more off the back side of her and left more in the front of the walk and push toy to show that she is going somewhere with it.
The third shot is a little too centered for my liking, but it's a good shot.
I agree that some could be brightened up just a tiny bit (not too much, just a little).
Overall, not bad shots, really.