Hey, Corinne. Yup, some people think apple cider vinegar helps with GERD. Those who hold that opinion believe that GERD is actually caused by having TOO LITTLE acid instead of too much. The reasoning is that if you don't have enough acid, the food just sits there in your stomach, giving it more time to reflux back up.
If you want to try it, buy a good quality ACV at a health food store (please, no Heinz). Look for the kind that contains "mother" -- natural sediment at the bottom of the bottle that has not been filtered out. Put a tablespoon in a cup of warm water with honey and drink. WARNING: Some people with GERD say ACV gives them the burn even worse. It's up to you.
I mentioned this on another post, but you may also want to try taking straight tablespoons of honey occasionally to coat the throat and esophagus. Of course, these are just suggestions I've come across in my own research and not intended to replace the advice of your doctor. Wow, cocktail onions. That's a new one. Glad it seems to be working.