The best way to evaluate a bird's body condition is to palpate the muscles under the chest, and the fill of the abdomen. A healthy bird will have thick, firm breast muscles, and a soft, full abdomen. Thin birds feel bony and skinny. Sounds like she may have trouble eating enough - either...
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Does it look like a fresh injury or an old one? Is she overly thin?
The biggest problem with break injuries is difficulty in eating and drinking. You will need to provide containers wide and deep enough for the bird to scoop up food and water with her damaged lower beak...