Hello, I'm Dr. Deb and will do my best to help you today.
I'm sorry that Zoey has hurt her leg.
There's a range of dosages for Deramaxx depending on whether we're treating chronic pain as might be associated with osteoarthritis or acute pain such as after a surgical procedure.
If I calculate the higher end of the dosage range for a 12 lb dog (which would be 3-4 mg/kg once a day), then her dose would be 1/4th of a 75 mg tablet, not to exceed 7 days of treatment at this higher dose.
You can split the Deramaxx you have into 1/4ths since the drug is evenly distributed throughout it.
I also suggest that it be given with food to avoid stomach upset.
Another option might be otc Aspirin although it's clearly not nearly as strong as Deramaxx. The dose would be 10 mgs per pound of body weight twice daily (also with food) or 1/4th of a full strengt, 325 mg tablet twice a day.
Neither drug should be given if she's vomiting, not eating or if she's also taking steroids (or other nsaid medication).
I hope this helps and that she's feeling better soon. Deb