Your vet should give you guidance, but yes, I would fast her 24 hours. But allow as much water as she wants.
So skip tonight's meal, and go ahead and start the Flagyl/Metronidazole tonight. Rice/chix breakfast tomorrow, and stay on that for a couple of days. Then SLOWLY ease back into the kibble diet, gradually replacing just a few tbsps of rice/chix with kibble per meal over the course of a week, until you're back to all-kibble.
This is all assuming her fecal tests were negative, of course.