Keep on speaking with the vet and if necissarying going in for another visit. Until more is known about the situation you should not take the problem so lightly, this could be some underlying cause that in the end might be deadly.
Your cat probably has better BM's on the lower end foods because there is much more fiber in it. This will make her stools much firmer.
As far as diahrea or constipation, smell goes, there is many attributing factors to that.
Chicken Meal is actually better then Chicken. But both are dependant on the source of the meat. If it's high quality, then that's wonderful.
It's possible to form an allergy to anything. It might be to some preservative which the food, or packaging of the food uses. It could be a excess vitamin etc.
You can try other foods which only have meat listed as Lamb Meal, or Fish Meal, etc etc. Try to stay away from listings that just say chicken or beef. That would defeintly be a good place to start to at least try and see if it makes any difference.
For now, keep kitty on the meow mix for the most part if you don't feel like trying a diet change, as it seems to keep her stabilized, even if it isn't the best kibble in the world, it's keeping her alive.
I'd see what you could do about getting pet insurance. Perhaps taht can help you with the bill.