Give your kid the Marshmallow test (http://en.wikipedia.org/wiki/Marshmallow_test - you can do it at around 4 1/2 yrs old), and video-record it.

It's a good diagnostic indicator of how good she is at delaying gratification, and more importantly, you can watch her display coping strategies. You may already think you have a sense of how they'll do, but it can be surprising.

It's also fun, in a torment-your-child kind of way.