Ha, she is a mart alack.. But at least she is learning..
Did you ever purchase the Book, "How Rude!, The teenagers Guide to Good Manners, proper behavior and not grossing people out?"
By Alex J. Packer, Ph.D There is copy here available for 55 cents. It is excellent.
I purchased it when our daughter was in 4th grade. It is wonderful.
http://www.amazon.com/s/ref=nb_sb_noss?url=search-alias%3...
Thank her for her reminders. Also let her know to give a moment for others to use their manners. She takes away the fun when she tries to beat others to use their manners. Remind her manners are not a game. They are a behavior, like raising her hands in the air at school. She does not raise her had first and yell "hey teacher" to beat others to answer the question. Instead people raise their hands and the teacher will then acknowledge a person..
Well now instead of correcting her all of the time, how about also thanking her or giving her good feedback when she does the right?
"I like how you are not talking with your mouth full." "Thank you for passing the rolls."
Also remind her that it is not going to be polite to correct people when she is eating out or at other peoples homes.
I am sending you strength.