Mobile Menu

I am using the Twenty Thirteen theme. The menu doesn’t seem to be working at all on a mobile device. I have set a padding on the menu (.nav-menu li a), but I don’t think that should be affecting the mobile version (the theme had a default padding anyways).

Any ideas? Any advice will be greatly appreciated.

Here’s the site:

http://www.katielynnfitness.com/

Thanks!