Hi, welcome to the forum,
amoxicillin allergy is known entity but
in her case it is other than allergy.
In some individuals, amoxicillin is known to cause thrombocytopenia, prolongation of bleeding time, hemolytic anemia. One thing also needed to be ruled out is bleeding diasthesis.
She needs to undergo complete blood counts, Prothrombin time, bleeding time etc. In 50 % patients cause remains unknown. This condition can be managed by discontinuing the drug and go for other alternatives.