Tara said in rec.pets.dogs.health:

Vet
suggested keeping her on it for a couple of days past what
the usual treatment plan is since her results showed she
was so strongly loaded with the buggers.

Even lightly loaded, the common advice for giardia seems to be
double the normal dose period. I hope the Flagyl/metronidazole
works for you (it provided only a temporary measure for Rocky
years ago).

Another option is Panacur.

--
--Matt. Rocky's a Dog.