Was Taking Amoxicillin For Tooth Abscess. Is Breastfeeding. Has Diarrhea. Can It Harm Baby?

Hi my daughter has recently had a baby and is breastfeeding , she has a tooth abcess and has been prescribed amoxcillin by her dentist ,she informed him she was currently breastfeeding and he said it was o.k. to take this medication , her midwife was also informed and she too said the medication was o.k. I called to see her today and she had been sick last night and her lower face and neck were slightly red and itchy we called the dentist who told her to stop taking the amoxcillin which she did immediately I have spoken to her this evening and she has dihorria ,I checked the meds on this site and am worried as it says this med may harm a nursing baby ? please advise what we do next ,many thanks