Honesty is the best policy. 1. Find one thing that is good about her. Begin with that. Something like, "I know that you are an outgoing and outspoken person."
2. Then, call attention to her mistakes indirectly. Say, "But, when people forget their manners and say insensitive and rude things, it upsets everyone."
3. Admit your own mistakes. Say, "I know that I must have said or done some things to upset you too. I know that I am not perfect."
4. Then, put your request into a question. Say, "But, Would you be willing to act politely and to think before you speak? " or "Would you be willing to not go to the birthday party?"
4. Then, let her save face. Say, "I believe that under the anger you are a good person."
5. Praise her if she has remained cool to this point. Say, "I know that you are reasonable and intelligent."
6. Make the mistake seem easy to correct and use encouragement. Say, "It is not very hard to get along with the family. The simple trick is to think before you speak. That way you will avoid hurting people's feelings. And, don't say anything at all if you feel like you will upset someone."
7. Then, make her feel happy about doing what you want. Say, "Let's help each other put an end to family fighting. If I begin to say something that will upset you then let me know, and I'll do the same for you, okay. I want to help you get along with everyone."