I'm pretty sure my bestfriend is obsessed with me. Creepy obsessed.?

She's always been a little "weird" and I've always admired that about her but lately things have just got a bit out of hand. A few nights ago I woke up to knocking on my bedroom window. It was about 3am or something and I saw her at my window, she was just staring at me and It really freaked me out. It's happened a few times since then and I don't know what to do. I'm certain that I was awake each time I saw her and the next day at school, she acts as if nothing happened, so I've been just hanging out by myself lately. She constantly calls me at weird hours and asks me really "personal" questions, ones that I wouldn't even share with my bestest of friends. I'm not making this up! So, please don't say that I am. I really need some advice on what to do or what to say to her. Please help me.