I have a best friend that I haven't seen in about 15 years and she lives 3 miles away. We've known each other since we were your age, but she had a type of emotional breakdown and will not answer my phone calls, emails, or knocks at her door. I let her know I still think of her, love her, and only want to talk to her and make sure she is ok, but she doesn't want me to see her. I keep trying, even though a lot of people who know me think I am crazy to continue. She will always be my best friend - so I definitely know how you feel. The only way I know she is still alive is that I have checked her mailbox and have seen mail addressed in her handwriting - so I know she still lives in the same rented house. Otherwise, it would be very hard to track her down and I would be checking the obits .
Just keep letting her know you how much you care!