There's something on-point about this neologism that points to the unique experience of being a child and a girl in "Barbie Doll." As countless authors have written about, girls feel a whole different kind of pressure from the adult world in comparison to young boys. And that pressure often has something to do with looking pretty and being on their best behavior while pleasing those around them, no matter if they end up looking and being someone they're not.
Lines 1-2: She's born "as usual" and goes around showing off her "pee-pee dolls" and miniature GE stoves. Immediately we sense the kinds of expectations that constitute being a "normal" young girl. The idea here is that girls should be in the kitchen, imagine being future mothers, and wear "wee lipsticks" in preparation for womanhood.
Line 15: Eventually the girlchild's good nature wears out like "a fan belt." All of the acting and pretending to be Barbie has essentially killed her spirit (and her body).
Lines 23-25: At this point the girl is dead but she gets a morbidly happy ending by being called "pretty." Of course we sense the speaker's sarcastic tone here, but the point is that these expectations for girls are not only absurd but also highly destructive and dangerous.