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If this were my dog, and she hadn't improved at all after giving her a bland diet, I would take her in to the emergency vet.
Dogs that have vomiting and diarrhea for any extended amount of time run a pretty high risk of becoming dehydrated, and the fact that your girl is already lethargic really concerns me.
I wish I could have given you a quick fix, but I think having a vet take a peek at her is the right thing to do at this point.
Good luck, and let me know how it goes!