She added me then deleted me instantly after. Why?

Recently there is this girl who happens to be best friends with someone I am close with and she has been doing some weird stuff to get my attention.

This girl has unfollowed me on Instagram, then liked my post on Fb. Then she goes on to add me on snapchat only to delete me 10 minutes later.

Why is she doing this and what should I do?
She added me then deleted me instantly after. Why?
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