Do not show anger.

 

Your anger is the result of fear.  Your niece senses this fear and is taking adventage of it.

Your fear may be due to not being listened to while growing up, and/or the lack of understanding shown by your husband.

It is your home.  No one should come in wihtout your permission.  Your feeling toward her does not need to be justfied to anyone.  You do not need to raise your voice, and your words alone are adequate enough.

Your husband may be distracted by your rancor toward your relatives.  But his indifference toward how you feel about this matter should not go unnoticed.  If he cares about the marriage, he should be happy to see her go.  Your attention should be more on him, less on her.  Again, do not show anger, which only exposes your weakness.  Explain to him that she may be a narcissist, and dealing with her will only get him burned.