(Hadley Hooper/For The Washington Post)

Q. My 10-year-old daughter is very confident, has many friends and makes good grades. But she is turning against a friend whom she has known since preschool. When this friend asked my daughter to play with her the other day, my daughter didn’t want to go to her house. She said that she “doesn’t really like” this girl anymore because she has gotten “kind of weird.”

We have gone over the “make new friends but keep the old . . .” adage several times, but I’m afraid that another good friend is telling my daughter which girls should — and should not — be her friends. My child tells me that this isn’t so, but the possibility still worries me.

I know that friendships often come and go during the tween and teen years, but what can I say or do to make sure that my daughter doesn’t become one of those “mean girls” whom I keep reading about?

A. You’re so wise to consider “mean-girlism” and to stop it before it starts, for it hurts the bully as well as the bullied, even though the bully may not feel bad about her behavior until she’s more mature.

Before you offer adages to your daughter, however, you should consider other possibilities, beginning with the language she uses. A 10-year-old is seldom as precise as an adult, especially if she can use a vague word like “weird” to cover up an embarrassing subject.

You and your daughter will probably have to have some long talks before you can find out what the word “weird” means to her. Have these talks in the dark or on a walk or when you’re cooking or gardening together. Your child will be much more confiding if she doesn’t have to look you in the eye when she speaks, if you leave long pauses for her to fill, and if you use slightly different words to repeat what you think she’s saying so she will have to express herself more clearly if you have misunderstood her.

Your daughter may be annoyed because she still likes to play with her dollies sometimes but her old friend only talks about boys, thinks about boys and dreams about boys. This is not because she is boy-crazy, but because the hormones of puberty arrive earlier in some children than in others and in varying intensity.

If you think that may be the case, you need to encourage your daughter to ask her old friend to a movie or a family picnic, but don’t expect them to enjoy each other’s company too much until they both share an interest in boys.

Or you may find that your daughter’s old friend is being weird because one of her parents has cancer or is drinking too much or because she’s afraid that they’ll split up. Fear can make a child angry or withdrawn or depressed or weird. But she’ll never tell a soul because she is sure that her classmates have perfect lives and she wants to pretend that her life is perfect, too. Conformity matters more to a schoolchild than almost anything else.

If none of these possibilities seems right, then your daughter’s new friend may indeed be misleading your child, just as you thought all along. If so, she needs to know that some children denigrate others because they are insecure, because they hate to share their friends, or because they think that they are popular only if they belong to an exclusive clique.

Your daughter will defend her new friend when you say that, but she’ll think about it — as long as you don’t say it over and over again — and she’ll probably change her mind eventually, especially if you arrange more important or more interesting things for her to do so she can’t spend so much time with this friend.

You must, however, teach your daughter to stand up for herself and to stand up to her friends, too, for this is the only way that she can ever be true to herself. Be sure to tell her how proud you will be if she invites a lonely child to sit at her lunch table each week, if she is kind to her old friends (and yours), and if she does unto others as she wants others to do unto her. These, she should know, are the values you lived by when you were her age and the ones you want her to live by as well. And indeed she will, because you have more influence over your child than anyone else. You just have to use it.

Questions? Send them to advice@margueritekelly.com. Marguerite Kelly’s next live Q&A is scheduled for April 21 at live.washingtonpost.com.