To be honest, I don't even know if animated GIFS even work in C2? But it doesn't really matter because animating in C2 is far better.
Don't bother creating sprite sheets, C2 creates these on export for you anyway. Simply select all the frames you want in an animation and drag them into C2. This is a shortcut for importing but you can always add/remove frames at any time.
Animating in C2 gives you the ability to control the animation and individual frame speeds as well.
The animation system in C2 is amazingly flexible. Often I don't use it for animation at all :)