What is the best drug to take for A Fib?

My mom is in her mid 50s and has bad diabetes (she can't ever keep her sugar levels under control). Anyway, she has been in the hospital for a few days because she was really sick with her gastroparesis and her blood sugar levels were very very high. Well, the doctor told her today that she had atrial fibrillation and they are going to put her on Coumadin. Well, I am very worried about her being on this medicine. I know she needs something to keep her heart from forming clots, but isn't there anything better than Coumadin? Please help.