A. Madeline, my 7-year-old, was a screamer too. With her it started a little earlier than 15 months, and thankfully lasted only six months or so (though it seemed longer). Here are two of the comments people "shared" with me and my husband during Madeline's happy screaming forays in public: "My, she's a very exuberant child," and when I was pregnant with Ellie, "You two are really brave to be having another." (Not to worry: Madeline is now mostly reasonable, as fair-minded as a Supreme Court justice, and still very exuberant.)
Here's what I learned not to do: Don't try to show her how bad it sounds by matching the volume of her caterwauling with your scolding. A screamer likes getting other people to scream, particularly the tall people with the (usually) controlled voices. Screaming for her is terribly exciting. It sounds different, it feels different in the throat, and best of all, it gets a reaction out of those around her.
Ignoring it never worked for us either. Madeline would just vocalize louder and longer -- and when we least expected it. Once in a while, when my husband and I were in a good mood, we'd answer Madeline's screams with pseudo-operatic arias, which would totally crack her up and at least make her try to scream more melodically. (She's a pretty good singer now, so maybe this is where it all got started.)
As for public displays of vocal prowess, you're just going to have to be prepared to step outside if a performance starts while you're in the mall or a restaurant. There's no hard-and-fast way to stop it -- you can try distraction with a toy or a book. Luckily, with kids this young, attention spans are as little as their sense of melody and volume control, so episodes don't last long.
Eventually, we noticed that Madeline had just stopped screaming. Anecdotal evidence suggests this phase rarely lasts longer than a few months. So your little girl will stop on her own, too. And then the screaming will be just a fond memory. But some things are better like that.
Contributing editor Trisha Thompson is a former editor-in-chief of BabyTalk magazine.