Yes, this sounds like sour crop. It's very uncomfortable, so a chicken will do neck gyrations trying to alleviate the discomfort.
Do not make your hen vomit. While it does give temporary comfort, the risk for aspirating the sour fluid into the lungs is too great. (Also, your hen will not enjoy the experience and will hate you.)
You need to treat the yeast infection that is causing the contents of the crop to sour. Nystatin is the best cure, but miconazole is cheap and easily obtained without a prescription. Find it in the women's hygiene section of the pharmacy.
You can use either the suppositories or the vaginal cream. Use about a quarter inch of a suppository twice a day for seven days or about half an inch of the cream twice a day for seven days. Give orally.
No need to massage, in fact massage may cause vomiting and aspiration. If impacted crop accompanies sour crop, which often these two conditions coincide, you will need to clear the impaction with coconut oil before treating the yeast infection. Massage is necessary to break up impaction.