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It is not exactly a poison, but can cause toxic reactions, depending on your individual dog's reaction to it and the amount. IThere is unfortunately no set "toxic dose" as each dog reacts different to it. It doesn't sound like your dog could've had much luckily, but signs to look for that it is affecting him/her:
constipation, vomiting, nausea (most likely this or nothing). But- in severe cases of large ingestion, can cause seizures (and in a rare few where tons are ingested, fatal.)
If you want to be on the safest side, go to an emergency vet for activated charcoal treatment, or keep a good eye on her and take her at the first sign of any symptoms. I don't mean to scare you, as this was a very tiny amount, but do think you should know what the lesser chances are as well. Likely, she'll be fine.
Best of luck. Let me know if I can help further.