Is getting too excited out of a sudden and crying the next moment normal?

Hello doctor,

My cousin keeps complaining about her looks. She says she does not look beautiful, but her sisters are beautiful. She is nice sometimes but suddenly starts crying or gets very excited. I keep telling my family members that she is undergoing some issue that needs to be sorted out, but neither her mother nor her sisters are willing to help her. They keep saying that she has been like this since she was born and everything is normal. But I do not feel so, and she has recently changed so much (though she used to say that she is not good-looking but has never seen her so intense). Is her behavior normal? What is happening to her? Please help me.