What Causes Red Spots On The Legs After Having Blood Transfusion?

Hello. Well, my girlfriend just recently had a blood transfusion about a week ago. We went to see her doctor who later found that her human globulin blood was at 5.3. We went to the ER and had a blood transfusion. In about 2-3 days passing of the blood transfusion she started to develop these tiny red spots on both of her legs. A day pass and more, another day pass and more. She says that she don't feel any sickness or anything. They're not itchy. What could it be?