If you feel her chest/lower neck on the lower, slightly right side, that is where the crop is (image below).
If she's eaten you will be able to feel food in there (the one in the picture below is quite full). In the morning when she hasn't had access to food yet it should be completely empty. If she's not eating well, it may be hard for you to find. But if food is remaining in it overnight and not emptying that would indicate a problem, or if it was very hard, or very large, soft and squishy. It's just another thing to check when you have a sick bird to try to narrow down what may be going on.
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