Please give more info to help the experienced folks figure it out such as:
What makes you think she had an impacted crop?
Typical Diet?
What do stools look like? Runny, color? Any blood in it?
Last time de-wormed?
Are they drinking and eating well?
Conditions they live in such as weather, how much space per chicken, etc?
Any respiratory problems? (can make them shake their heads)
Any odd breathing such as gaping?
Age?
How many birds do you have?
How long you have them?
Any new chickens added recently?
Are the hens laying eggs currently?
Are they vaccinated for Mareks Disease?
Giving vitamin supplements and electrolytes may help for now until you know. If not eating well try some scrambled egg.
Any other background info would help! I am not an expert myself so hope someone will see this!