What does it mean if a girl you know randomly sends you a friend request?

Question

I noticed I got a friend request from my best friend sister. Which I find it real strange since we dont talk, to each other a lot we always have small talk we, been knowing each other for years now and until today she sends a friend request. I don't want to tell my friend this because he might not believe me ,and if I accept this he might get mad for accepting his sister.

Answer 1

Maybe accept it, but dont interact with her?  Idk.