What could cause my aunt to be denied a platelet transfusion?

May not b approp: Depending on the cause and degree of thrombocytopenia a platelet transfusion might not be apprpriate and for some diseases like thrombocytopenic purpura giving platlets is like pouring fuel on a fire and should be avoided.

Diagnosis: Platelet transfusions are not recommended if counts are above 50,000/uL unless brain or eye surgery is expected. Other contraindications include TTP(thrombotic thrombocytopenic purpura) HIT(heparin induced thrombocytopenia), not useful for ITP(autoimmune thrombocytopenic purpura). Indications are for dysfunctional platelets and active bleeding, and counts below 10,000/uL.