Hi BellymonsterMom,
I'm so sorry you and Bella are going through this.
Here's an article published by a site I've not used before,
Cuteness. Having said that, this article says "Hypersalivation -- or excessive drooling -- is [a] common" side effect of metronidazole.
Metronidazole Side Effects in Dogs
Crankin' up the thoughts and prayers for you and Bella.