The anti-yeast meds will calm the sour state of the crop within a short time. I've never had a hen "urp" the miconazole.
As
@casportpony touched upon, there are mitigating circumstances, though relatively rare, where a sour crop will not respond to an anti-yeast treatment. I had such a hen very recently. She appeared to have a bacterial infection of some sort and that was probably causing the sour crop. It's very tricky to treat a bacterial infection while also treating sour crop as the antibiotic aggravates and sometimes causes sour crop.
My hen responded to neither the antibiotic or the anti-yeast med and I had to euthanize her. But I've otherwise had excellent luck curing sour crop with miconazole. Be sure you treat twice a day for a full seven days.
As far as feeding your patient, you may offer her boiled egg and anything else other than starchy foods as you see her appetite return. Generally, a sour crop patient won't have much of an appetite the first day of treatment, but you may certainly offer her the food.