It looks like your sentence got cut off there at the end. Did you mean to say something like "... at high school" or "... at the harbor"? Without the full context, I can't be certain what you were trying to convey.

If you're saying Christie was one of your best friends in high school, you could finish the sentence this way:

"Christie was one of my best friends at high school."

Is that what you were getting at? Or did you have something else in mind to complete the thought? Let me know if you'd like to revise or expand on that statement.