Hi there and thanks for your question.
It sounds like you are having a frustrating problem with your daughter's dog!
There are a few things I can think of that may cause these symptoms.
First of all, this may just have been a very strong bacteria that needed a longer course of antibiotics. If this is the case, then she should do just fine.
Next, you may want to ask the vet about the possibility of hypothyroidism. Dogs with thyroid problems can have repeated skin issues.
Some allergies can make a dog prone to skin infections as well, but it would be quite unusual for them to come on all of a sudden like this.
Most likely this is just a nasty bacteria and will take several weeks of antibitoics in order to be cleared up. If it is not clearing up you may want to have a culture done of the infected area to make sure that it doesn't need a combination of antibitoics in order to heal.
The above is given for information only. Although I am a licensed veterinarian, I cannot legally prescribe medicines or diagnose your pet's condition without performing a physical exam. If you have concerns about your pet I would highly advise contacting your regular veterinarian.