3–4 days is exactly the right amount of time for an infection to develop, and/or for her to be having a bad reaction to the antibiotic. I would be very concerned. Please get her back to your vet and have them check for signs of deep infection (fever, dehydration, diarrhea, localized pain, etc.). A follow-up visit should have been scheduled already, but they may have said something like, “Bring her back i a week.” You need to get her in now. Please! If it’s something minor, you can fix it right away, but if she’s on her way to sepsis, it will kill her without aggressive treatment.