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1. When was the ingestion?
2. What is the mg of Oxycontin ingested?
You may want to make her vomit since the ingestion was so recent. It probably wouldn't cause much more than just some sedation if you let her ride it out but it can cause respiratory depression that is better avoided.
To make her vomit you can give her 1 tablespoon of hydrogen peroxide orally. If she doesn't vomit in 10-15 minutes you can repeat the dose. It may help to give a small amount of food (1/4 cup) prior to giving the hydrogen peroxide.
Let me know how it goes.
That's the only "safe" thing to use that you would have available.
In that case, I would just let her ride it out. You usually will see signs within 4 hours and the half life is 10 hours so by early afternoon she should not have any further signs. The main things to look for would be respiratory depression (slow, shallow respiratory rate or difficulty breathing). At this dose I would be very surprised if you see it but just be on the lookout.
The other option is to go to your local ER vet and get a dose of Naloxone into her- this is a reversal for opioid medications and can be used if any signs are seen or to prevent signs.
I think she'll be fine, but those are your options.