Dealing with an angry friend?

Try to talk to him/her calmly.
Find out the reason why she is angry with you. If it's really your fault,then sincerely apologize for hurting her feelings. If she is willing to talk about it, listen carefully to what she is saying.
If she is not willing to talk, then back off. Talk to her some other time. Let her/him have a good time to think about it.
If you feel that the friendship is worth saving, then be sure that your friend knows your feelings.