my sister

Through recent years I have become concerned with my younger sisters behavior. She gets very irrational and cannot control her emotions. She can go from one of the emotional spectrum to another in a short period of time. I am attempting to learn as much as possible to see if this seems to be a symptom of something. She seems to be growing more and more irrational in her behavior with others. For example, she will yell scream and cry at the drop of a hat if anyone says anything she does not like. Her behavior is really beginning to worry me. If any of this sounds familiar let me know I really want to help her out.