How do I contact a friend on Facebook if they won’t accept my friend request?

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One week back I found my a classmate’s ID on Facebook. I have sent her friend requests, even messages, but she doesn’t respond. When I search her name it shows 2 mutual friends but when I open her ID, the friend list shows up empty.

I need to talk to her on a serious matter and her Facebook ID is my only hope. Please help me regarding this!