She's not part African American.
i just checked her imdb bio and it says she is of caucasian, filipino, and north african background which is not the same thing as african american. i also checked out her wikipedia page and it mentions her grandmother as caucasian and her grandfather as being only filipino. plus, in this article it mentions that hailee's rep denied that hailee's mother is part african american.
http://www.hollywoodreporter.com/news/black-thor-actor-blasts-debate-164048