I just read some more about it. Seems to be a lot of disagreement/confusion in the literature. Some say that a sour crop has become too acidic, so instead of ACV to increase acidity, do the opposite by giving baking soda (dissolved in water) to reduce the acidity. Some do say that impacted material must be removed by either massaging it down towards the next part of the GI tract (not vomiting upward), or surgically removed, if the bird doesn't pass it on his/her own. I would guess that many of the "cures" we read about with ACV, yogurt, etc., just appeared to be cures because the bird happened to pass the stuck food. Administering some remedy during that period of time does not prove cause-effect relationship.
OP, I would ask your vet why she thinks it's a bacterial infection, rather than fungal. While most online sources seem to think fungal, some do mention bacterial infection. So if your vet has a good reason to think bacterial and not fungal in your particular case, I would continue to take her advice.