My cousin gave me the silent treatment for almost a year?

Hello I need answers. Last summer 2010 my cousin was supose to come to my house after my birthday but at the last minute she desided to let me down and she desided to go see a concert she tried to call me back to tell me she would come but I hung up on her I said no go see the damn concert...I was hurt and angry but now I'm more hurt cuz my cousin gave me the silent treatment next week it will be a year we have stop talking and we were close. During the holidays 2010 I saw her but we didnt talk or look at eachother it was cold . Its still cold. There is a wedding in july my other cousin is getting maried...and she will be there it will be awkward to talk to her again since its been a year . I dont have the courage to go up to her and say sorry. I'm still hurt cuz she gave me the silent treatment . I know I will see her at the wedding but once I do I dont know what to say to her I'm so stressed out these days cuz of that and my parents knows that I dont want to go cuz of the situation. I'm still not going should I go and make amends with my cousin. She is very important to me it feels i've lost a piece of me...I cry a lot cuz I regret and I still think I dont deserve to be forgiven...