Nellie isn't her real name, but Steinbeck couldn't remember her actual one—so this is what he comes up with. We don't get the sense that Steinbeck was impressed by her or her antics, since his description is far from flattering or reverent:
The name was not Nellie. I forget what it was. But she shoved through the dense crowd quite near enough to me so that I could see her coat of imitation fleece and her gold earrings. She was not tall, but her body was ample and full-busted. I judge she was about fifty. She was heavily powdered, which made the line of her double chin look very dark. (4.3.36)
He doesn't editorialize too much, but between the imitation fleece, the overdone makeup, and the double chin, she doesn't come off as particularly attractive or tasteful.
Beyond the superficial stuff, Steinbeck gets a nasty vibe from her (shocking, we know, given that she's there to shout at little children): "She wore a ferocious smile and pushed her way through the milling people, holding a fistful of clippings high in her hand to keep them from being crushed" (4.3.37). So, even before she starts screaming at kids, she comes off as brutal and pushy.
Oh, and by the way, those clippings are newspaper articles about the Cheerleaders, and the crowd lets out "squeals of delight" (4.3.38) at seeing themselves and their nonsense in print. So, there you have it—the world's first reality stars, right? Apparently, the Cheerleaders are more focused on the fame than the ethics of what they are doing to get it.
Then, of course, the school arrivals start and the women go crazy, not just over the African American children, but the one white dude who is willing to bring his child to school that day. Steinbeck is horrified at the frenzy that erupts: "No newspaper had printed the words these women shouted. It was indicated that they were indelicate, some even said obscene. On television the sound track was made to blur or had crowd noises cut in to cover. But now I heard the words, bestial and filthy and degenerate" (4.3.44). So, yeah, in short, Steinbeck is less than impressed with these women's "protest" and their approach. In fact, he is shocked and nauseated, concluding, "These were not mothers, not even women. They were crazy actors playing to a crazy audience" (4.3.45).