I'm grabbing at straws here, because I'm new to chickens, but I've been raising parrots for 20 years - and with parrots, the word "impacted" implies an obstruction of some sort. I'm not so sure its an obstruction - could be, but maybe not.
I've only ever seen crops that big in birds with "slow crop" which is normally caused by a yeast or bacterial infection, which prevents the food from being digested. Some call it "sour crop," but either way, the bird is hungry because it isn't digesting its food, so it continues to eat, and the crop continues to grow because the food isn't going anywhere. All this food just sits in the crop and goes sour with the yeast or bacterial growth. The bird will eventually stop eating and die without medication.
Is her crop really soft like a water balloon? Do you have someone that can take a swap of the crop and test for yeast or bacteria, or look for an obstruction? If you have a chicken vet, you will probably want to make an appt. ASAP before she gets weaker. You could remove the contents of her crop and flush it out by going down her throat with a syringe and a crop needle, but that takes experience - if you go down the wrong "pipe" you could kill her. Do NOT cut her open - anesthesia is required for that, and not only would it be painful, but it would kill her for sure.
Kathy