Allergies

My step daughter turned 2 this last July.  A few months ago she was prescribed Augmentin, and she developed a rash in her groin, and gave her acidic stool with caused her butt to bleed.  It was listed as an Allergy due to the rash.  Her mother refuses to believe that this is an allergy, and has allowed other pediatricians to prescribe it to her at least once, claiming that she has taken her to three pediatricians to "test" her for an allergy to Augmentin, and they said that she is not allergic, and that a "rash" is not considered an allergic reaction.  My question is, what possible serious side effects could occur if her mother continues to allow her to be put on Augmentin, and is there any action we can take against her for it?

[JuneSunflower]

Why is she taking Augmentin?  Isn't this an antibiotic, so it should be a short-term med?