How can one moment take your friend away?

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My best friend and I have been so since we were about 7. After we graduated from high school we both went to different colleges and I made new friends but obviously no one can replace your best friend right. Well, life took us in different directions and we didn't talk as much but we still would be there for each other if anything happened. Her mother got sick and was in the hospital so I came home to be there for my friend. (At this point I live six states aeway). I took a week off work and stayed with her. Her mother got better and they let her go home from the hospital. Then about 2 weeks later she died. I was devistated because she was like a mother to me to but I could not get off work to go to the funeral. I sent a card and kept trying to call her but she wouldn't take my calls. Her sister said she was mad at me for not coming down but I couldn't get off work again because I just took a week off two weeks prior. Man, so now it's 3 years later and she hasn't spoken to me since. She missed out on my wedding, graduation from school, and I'm sure she's had some things I've missed out on as well but she still won't talk to me. What should I do?