Narcissistic personality is constantly seeking about personal attention and selfishness.
One cannot change behaviour of this kind of person right away.
They think they are the only one who are best and have something like Bossy rights to admire.
But if it is in your mother then it's a total opposite situation than for any other men or women.
Mom surely can have this feeling of selfishness but you can't just simply argue with her.
You must understand that she is yours and she is critical behaviour.
So, if you want to deal with her you must focus on these points
1. Never try to change her
2. Don't argue and Don't be rude with her
3. Must be in her support otherwise she will get worsen.
4. Constantly try to love him but don't be so picky
And if the situation is too bad , I would suggest you to keep distance from your narcissistic mother.
But, Don't separate yourself from her, after all , she is your mother.
Now decide yourself whether to argue with her and try to change her or to be thankful that you at least have your mother and her, not much, but small love is enough rather than not having it.