the vet should be doing proper tests mate .
my 2nd vet told me its not normal for a dog to pass solids more than 3 or 4 times a day (on average, taking into acount the amount of food he should be eating)

i would go to a different vet and get her checked out again (it wont be cheap) they will probably keep her in for observation but it will be worth it in the end .
my mastif was sorted after a few weeks with trial medications and different diets (some times it gets VERY messy). I ended up feeding him chicken tit and rice for a couple of weeks untill his digestive system sorted itself out and then he was able to hold his bowel movements and ended up doing 2 normal shits per day