Anger issues and low EQ
Doctor Answers (2) on Anger issues and low EQ
Since your sister is quite young, these kind of anger outbursts can be indicative of numerous health conditions ranging from minor adoloscnece issues, personality disorders, to Bipolar disorder.
Also, the onset of most psychiatric illness is seen in adolescence and early adulthood (15 to 25 years of age) and most amenable to treatment with early intervention.
Therefore do not ignore these symptoms and get her to a Psychiatric professional at the earliest. It could be a trivial issue that triggers these outbursts, which a professional ear can identify and educate the family members abou it.