Admittedly, an unconventional and inspired choice.
As these photos illustrate, she has the appropriate appearance and poise to pass as this character. But you need more than the look to pull this off.
Fortunately, Katie’s recent performances in Thank You For Smoking, The Kennedys How I Met Your Mother and Don’t Be Afraid of The Dark indicates she has become capable of the gravitas and elegance necessary in portraying Wonder Woman. Her acting began to significantly improve with Batman Begins. Until then, she always seemed to be doing Joey Potter from Dawson’s Creek.
Of course, she would need training to build/tone muscle, as well as martial arts.