Hi, Your daughter seems to have developed a hematoma. While donating blood, either the needle or the plastic tube covering the needle most likely bruised the vein wall which caused extravasation of blood into the tissue. This is seen on the outside as a swelling or lump. The risk of infection is low because single use sterile needles are used for blood donations. Apply ice to the affected area to reduce swelling. Use ibuprofen and tylenol for the pain. Elevating the arm also helps to reduce swelling. Even if no treatment is used, The swelling should resolve in two or so weeks. It is unlikely that she has an infection, but If she develops any of the following, do consult your doctor: Fever, redness of the skin that is enlarging in size. If the lump is increasing in size. Get well soon. Hope I have answered your query. Let me know if I can assist you further. Regards, Dr. Felicia Manickam