Somehow comic book artists got it in their head, maybe since the time of Dan DeCarlo, that when a female is first rendered with a specific hairstyle she is always sporting that look. Think Iris West before she married Barry "the Flash" Allen, she always wore it in a bum. Or Janet VanDyne with her trademark short hairstyle which never wavered below the shoulders.
And these two lasses, Betty Cooper and Vicky Grant. Oh sure, they had the power to transform temporarily into superheroines and were both teens. But their defining trait was the ponytail look. Or in Vicky's case, her perpetual pigtails which she was never seen out of (until a goofy modern appearance). At least Betty shifted it from back to the sides to back again. Yawn.