Since she is still so little, could certainly be coccidia or giardia.
When I went through this with Oz, they ruled out both of those. But believe me when I say I know how scary this is. It's just NOT normal.
Even the vet said that while seeing this kind of thing occasionally, it was still unnerving to them.
Ozzie was diagnosed with HGE. (hemorrhagic gastroenteritis) He had a bout in November and another in February. Flagyl is one of three meds he was one. In both instances, he was much improved within a day or two. (He DID have to stay in the hospital both times, however.)
The upside is that while trying to find out more info on HGE, I found YorkieTalk!
No matter what it is, I sure hope Tatum is well again soon. You definitely deserve a break. Thoughts and prayers for both of you.