Sorry to hear Sadie is doing all that vomiting! Has your vet done any bloodwork or taken any x-rays?
OK, well I think that is where you need to start, rather than just trying various things. Problems like kidney failure can cause vomiting and nausea and would be treated differently than with a grain-free diet or acid reducers. The other possibility is dental disease, which can cause excessive drooling. If she has a lot of tartar or red gums, then having them cleaned and any diseased teeth extracted should help a lot. X-rays can help look for any growths that might be pushing on the stomach or intestines.
I think dental disease could cause the vomiting, partly from pain and partly from just swallowing all the saliva.
I think since you've been trying various things with no real success, it is time to move on to further diagnostics. If you catch something early, hopefully the cost won't be as much.