Why do I always dream of one particular classmate?

There was a girl I went to elementary and middle school with and we knew each other, and talked but I wouldn’t say she was a friend though. I’m 30 years old and for years she has popped up in my dreams. What does this mean? I ran into her twice over the years in grocery stores. Why this particular person is in my dreams? My real best friends don’t even show up in my dreams.
Why do I always dream of one particular classmate?
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