Ah...now makes sense.
Well, was it illegal? Yeah, it probably was.
Was it risky? Yes
Certainly, she would have the knowledge to choose a particular antibiotic for a particular concern for your son.
However, if there was ever a dosing error, the duration of antibiotic was not used long enough to help avoid future antibiotic resistance issues, or imagine if there was a allergic reaction! She would be in a load of trouble.
So, it was not entirely smart.
I certainly have heard of stories where a vet self treats themselves. Wise, probably not.
I just received a bite wound to my leg about 3 weeks ago. I could have just grabbed clavamox off the shelf. did i?
Not worth the risk!
So illegal? Well, as a criminal would say, only illegal if you get caught.
Smart? Definitely not. Treating your own son is risky business.
Hope that's a fair answer.