Dogs can be prescribed Prozac, but of course the dosage varies from the one for humans.
"Side effects associated with fluoxetine include lethargy, panting, hyperactivity, shaking, restlessness, excessive vocalization, aggression and temporary lack of appetite. Gastrointestinal upset may also occur.
When large quantities of fluoxetine are ingested, pets may seizure. Overdose should be promptly treated by your veterinarian.
Medication should never be administered without first consulting your veterinarian.
For dogs, the dose of fluoxetine is 0.5 to 1 mg per pound (1 to 2 mg/kg) given every 24 hours, orally."
If your dog weighs 15 lbs., she would have ingested about 5 mg. more than necessary for her body weight. She might appear lethargic, or exhibit any of the side effects you see listed, but to err on the side of caution, I'd have her evaluated by an ER vet center, ASAP.
If you think she ate this pill less than an hour ago, you can induce vomiting with 1 teaspoon of 3% hydrogen peroxide to the back of the tongue. This can be repeated 3 times, if she doesn't vomit within 20 minutes after the first dose. Bring her outside after you give the peroxide, to walk her around, shake up her stomach contents, and it will be less messy outside if/when she vomits. Look for the capsule, if she vomits.
"Three percent hydrogen peroxide is quite effective in making dogs and cats vomit. You must be sure to use three percent peroxide and not hair coloring strength peroxide. Despite the label indicating that hydrogen peroxide is toxic, it is safe to give to dogs for this purpose. It is considered toxic since it induces vomiting and therefore does not stay in the body. The appropriate dose of hydrogen peroxide is one teaspoon per 10 pounds of body weight. If you have an oral syringe, one teaspoon equals 5 cc or 5 ml. Once given, walk your dog around or gently shake the stomach area to mix the peroxide with the stomach contents. Vomiting should occur within 15 to 20 minutes. If no vomiting occurs, you can safely repeat the three percent hydrogen peroxide once. If it is still not effective, your dog may need to be seen by a veterinarian for stronger vomiting medication.
Once the hydrogen peroxide is given, it is important to watch your pet so that he does not re-ingest the substance. If there is concern about toxicity, collect and take a sample of the vomitus to your veterinarian."
I hope your dog will be fine!