My mother is driving me a little bit crazy with how to address invitations. I'm admittedly compulsive about wanting to do everything with proper etiquette that Miss Manners would approve of, and I'm having difficulty reconciling my mother's rules with Miss Manners. For example, my mother insists that I address the outer envelope to my sister and her husband as "Katie and Charles Matthews" instead of "Mr. and Mrs. Charles Matthews" because she says the latter doesn't even recognize my sister. She also says I should address the inner envelope of my siblings and other close relatives as "Katie and Charles" instead of "Mr. and Mrs. Matthews" because she says the latter is too formal.
She also refuses to give me the address of my dad's friend's girlfriend and says I should put them both on the same invitation with my dad's friend's name first even though his girlfriend's name comes first alphabetically. Her reasoning is we wouldn't be inviting her if she and my dad's friend weren't together.
My mother seems to think people will get offended by my following the rules. That seems unrealistic to me. At worst they can say it's a stupid rule but not think I was trying to slight them. Should I do it my mother's way to make her happy? Should I do it the Miss Manners way? Or, should I do it the Miss Manners way and tell my mother I did it her way (and hope she doesn't find out)?