I'm guessing that this chick could have an impacted gizzard that's backing up into her crop, not permitting the crop to empty. Treating a gizzard is a lot trickier than treating the crop, and honestly, it doesn't always work. But I suggest you try.
Do you have molasses? A narrow oral syringe? It may be time to try a molasses flush to get the gizzard moving. One teaspoon molasses mix into one-fourth cup warm water. Then give it to her with the syringe.
An easy method is directly into the esophagus which will get it into the crop without it going all over the chick and you. The esophagus is located on the chick's right side of its throat. The airway is in the center. Putting the syringe directly into the esophagus avoids the risk of getting liquid into the airway and having your chick choke to death. But be careful no to overfill the crop. Doing this in several phases an hour apart is best. Here's a picture of what you'll be doing:
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