Hello there and welcome to BYC!
Yes, sounds like she has a sour crop. You will need to keep her confined or at least so that she cannot eat anything but her chicken feed. No hard seeds, grains, grass or anything hard.
Tomorrow morning, first thing before she eats or drinks, check her crop. Compare it to the others if you are unsure, but it should be completely empty. If it is soft and squishy, it is either slow or sour. You will need to get that gunk out of her as what is in her crop is becoming toxic.
So take her outside and hold her like a football in one arm, beak out. Support her with your other hand at the crop. Lean her forward, beak down. Gently massage and squeeze the crop. The MOMENT the fluid starts to come up, count to 2 or 3 and than stand back up. No longer as you can aspirate her. Give her some time to catch her breath and do it again. You will never get it all out, but do these sessions repeatedly until you can't get any more out. Then keep her confined so she can't eat anything she should be eating.
Dampen her feed. Chickens love damp feed and this will also make it easier to digest. Put some probiotics in her water. Human grade stuff works just fine. Just empty a capsule into a plastic quart waterer and discard the capsule. Fill with water and make a new batch daily.
No oil. Some people will tell you to give them oil. Oil does nothing but slow the crop down even more.
You can also mix some plain yogurt into some chopped hard boiled eggs. These she can have and is a great way to get good bacteria into her crop and tract.
Keep this up for a few days. Vomit in the mornings, no hard foods, damp layer feed, probiotics and yogurt on some hard boiled eggs.
If the smell of her breath gets really bad, you can add some fungal meds to the mix and that should clear this up.
Good luck and I hope you can get her healed up soon!
