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I'm so sorry to hear your dog's stomach is upset.
It may be difficult to treat at home if she continues to do this or is not able to hold anything down. However, you can try as long as she isn‘t painful, pale, overly lethargic, bloated appearing, straining to defecate, excessively panting or unresponsive (which requires more immediate vet attention).
Wait at least 12 hours before feeding, a bit longer if still gagging. Then try giving some pepcid at a dose of 0.25mg per pound of body weight, as long as your dog has been fairly healthy otherwise (no liver/kidney disease or on heart medications). Then after 30-45 minutes, you can try very very small amounts of a bland food, like baby food (chicken or turkey flavors are good) or boiled chicken. Just about a tsp or so.
If she holds down, try again in an hour this same amt. If doing ok, do this for a few hrs, then about 1/2 a meal amount for his next meal time. You can repeat the pepcid in 12 hours as well, if you feel it is needed (while the bland diet helps the most, the pepcid may help speed along the GI's settling).
Keep on bland diet for a couple of days, the gradually switch back to normal food. If she's not able to hold down the pepcid or continues this behavior, she'll need a vet visit sooner than later, as injectable medications will be called for, and further diagnostics may be needed to see if this is more than just a stomach upset.
Often antibiotics are needed for the bacteria that has built up in the GI tract. Also, make sure she's drinking water or even some unflavored pedialyte the entire time so as not to dehydrate, but only small amounts at a time after fasting, and keep her away from heat and indoors while recuperating, away from eating any grass, and inside except for short leash walks only to do her business.
Here's some more info about Pepcid. If any concerns, it is always best to check with your vet before giving (you can certainly start the bland diet protocol and add Pepcid later if needed after speaking to your vet):
Best of luck, hope your dog is better in no time!