You dog is small and her stomach is getting empty with acid building up. She just needs to eat a bit later at night before bed, OR have something to chew on over night.

Apples, carrots and sweet potatoes (all 3 raw) are wonderful dog treats!

But as mentioned above, something with a bit of fat will be better for this issue. The fat slows the digestion process and keeps something in her tummy for a bit longer.

I can't believe a vet actually saw her THREE TIMES and likely charged you THREE TIMES for this!

she may do better as she grows; but she is a small breed and sometimes you just have to plan to give them something later in the evening. Sugar LOVES her peanut butter treat each evening! I buy Teddy's Old Fashioned Peanut Butter, unsalted. It is all natural, so you aren't introducing any preservatives and such; it does have to be refrigerated after opening. I take a little clump - like a small tiny meatball - and give her that on my way to bed. YUM! Our problem was solved.

I hope yours can be solved easily, as well!