Suggest Treatment To Cure Red Lump On Arm Caused After Blood Was Drawn

My co-worker just had 5 vials of blood taken. She is on coumadin. Her arm now has a very dark red circular lump on her arm. It looks awful and is about the size of a nickel. She is putting a cold compress on it. Should she do anything else? This has never happened to her before and she goes to the lab for blood work just about every week for the last year (since she's been on coumadin).