Try to get her hydrated with sugar water, electrolytes. Watery chicken feed could be offered after she is drinking. What do her poops look like? Could she have been injured? How hot has it been there? Do you have more than one water and feed station and is she in a mixed flock with other breeds? Does she have any food in her crop? Is she low in pecking order? Hopefully, it is just dehydration, and not something more serious such as Mareks. Coccidiosis can cause extreme weakness, so it should be also considered.