I reposted and no one answered, please answer?

I'm not going to say you're too young, but I am going to say she is acting this way because of her age. At your age, friendships are really important to people. Maybe she doesn't feel super close and comfortable enough around her friends and she has her guard up when she is with them so she treats you differently because she is afraid of what they would think of her. It's really all about her friends in this case because if you and her are normal when you're alone, then you obviously like each other. But like I said, she is still immature because she is only 13 so she is going to act differently when she is with her friends whether it's to fit in with them or make sure she can keep them.