Wonder Woman made her debut in 1941. Like many DC and Marvel superheroes, she's existed in many different forms and one storyline's canon doesn't necessarily exist in another comic book line. Historically, when Wonder Woman was created, she was considered by her creator William Moulton Marston to be stronger than Superman. But the difference was that she stood for something he didn't: peace. 

Whereas we consider Superman to be a symbol of protection of a world that isn't his own, Wonder Woman was a symbol of peace. She and her sisters were symbols of a movement against the "masculine" concept of aggression being the only way to solve world conflicts. That being said she was powerful, but she was powerful enough to not use her powers. 

In the early years, there isn't a clear answer if she's bulletproof or not, but it's assumed to be a fact that she is. However, in Justice League #42, we got a very different answer. As Superman and Wonder Woman are pelted with bullets, one ricochets off of the Man of Steel and hits her in the throat. At the very least, this version of the hero is very much not bulletproof.