What will you do if you have a sister who treat you badly?

The other day I read an article about what's going on between two sisters. Jennifer (J)and her elder sister go to the same high school, they used to get along really well, but lately she's been acting like J is her worst enemy. J don't know why and ask for some advice.

After reading it, I think it's normal for sisters to argue and get irritated with each other for the most random reasons, but it doesn't mean her sister doesn't love her. Maybe she feels a little upset and stressed since they two are at the same school. See, the school was hers before it became J's. She could feel jealous that her younger sister has more friends or do better than her. She might not even realize she's acting so badly to you. I think J can talk to her sister about it face to face and ask what she can do to make it better for both of them.

If you were Jennifer, what would you do? Get angry, cry, fight back or just keep silent?