Dakota Johnson is the young Hollywood starlet who gained prominence for her role in the '50 Shades of Grey' series of movies. She's also had some success in the romantic comedy genre. She has a great way of playing the every-girl, especially one who is slightly socially awkward. Now that may all sound like she's a very odd choice for Wonder Woman, and I agree, but imagine what her vibe would bring to the role. There's a lot of vulnerability that Johnson can portray in the character.
As much as Wonder Woman is self-assured and strong, she's also a fish out of water. Dakota Johnson could accurately portray the comedy and awkwardness of going from Themyscira to venturing out into the rest of the world. Ultimately, producers thought her overall vibe is off for the role though.