Yeah the chick who actually posted the comment in question has came out and said she isn't a plant & everything is a coincidence. Her explanation is pretty plausible, imo.Other plausible explanations:
Lurker, who signed up to post after typing a message.
or
Somebody with a novelty/offensive/stupid name who knew that the President would never respond to any question, no matter how thoughtful, from such an account, so they made a new one.
Reddit user says she didn't plant softball question for Obama, but wishes she had | The Verge