Looks like her crop. If it's like that all the time, then she may have a crop problem, like pendulous crop. But if it looks like that sometimes, and it's gone others, then it may be completely normal. Some birds eat a lot and really fill their crops and they can look very large at times. The crop is kind of like chipmunk cheeks, it fills while they eat, and then slowly empties into her digestive tract. Check her crop first thing in the morning before she eats anything to see what it's like. It should be empty then. During the day it will fill and empty as she eats and digests. If it's not empty in the morning, and feels very hard, or very soft and squishy then there may be a problem. If it's empty in the morning she's probably just fine.