It seems she is finished with pretty baby sounds, and over the past couple of weeks, all her coos have been replaced with “arrrrgh…rrr…grrrrrrr…” and other curmudgeonly noises.
The neurotic in me keeps wanting to run quick Internet searches (it’s too easy!) in case this is some kind of developmental red flag.
But, no. I think, after all, that the thing to do here is just to growl right back. And to laugh. Because it’s pretty funny. Especially if she’s dressed in pastels or polka dots or other incongrous things.