It's wonderful that you are willing to help. However, you'll need to be sure to involve a health care provider (probably the baby’s doctor) who can screen you for infections and viruses. Your milk may need to be screened as well. You'll need to avoid smoking or taking any medications or herbs while you're providing milk.
It might also be a good idea to contact your nearest milk bank to see if they can answer some of your questions, help you coordinate the direct donation, or if you could donate milk to the bank in exchange for your friend receiving pasteurized donor milk.