1. Give him/her enough free time and freedom. Anger diminishes with time. 2. Say sorry and accept your mistakes. 3. Send him/her Flowers. 4. And if it does not work, make new friends.

Nacir gives good advice. I think it depends on why she's angry. If can address the reason for her anger in a way that satifies both of you, then you will have a better chance to repair your relationship.