If you've gone through the online YC application process, imagine you dumbed that down for a 10 year old who only had 10 minutes to complete it and only had to answer one question, along the lines of "Why is America the best country on Earth?"[0]
Here's the rejection email my wife got for those that are curious:
Thank you for applying to the Female Founders Conference. Unfortunately we couldn't accept you this year. There was such a large number of applications that we had to turn away hundreds of people we would otherwise have accepted.
We will be streaming the event live on our website, and are looking into options for even larger venues in the future. We really hope you will apply again.
Best,
Y Combinator Team
http://femalefoundersconference.org
[0] Bonus points for anyone who gets that reference. :)