Does she look like a pitbull to you? She looks like she could be a mix to me but I am not an expert on Pits.
This guy was about six months old when I took this picture.
Here's three together; See how long and leggy the dog on the left is? The puppy in the middle is already almost as tall as him, but quite a bit thicker. The dog on the right is short and built like a tank.
This one's kind of hard to see, but the dog behind that guy's leg is a registered pulling dog; Probably weighs about 40 pounds. The other one is a four or five month old puppy.
This girl was rescued from someone who cut her ears off with scissors. She's what most people would easily identify as a pitbull.
And this is my mix with another full grown mix.
It's just really, really hard to tell. Behavior combined with appearance is a better indicator.