The girls in question here are mainly upper class. The article points out that “75 per cent of [their] parents are training their daughters for lives of leisure, to make a business of leisure, as it were, to lead a life of organized up-to-date play” and says “it is no more fair to condemn these girls for their extravagance than it is to blame the messenger boys for getting into the juvenile court. The standards of both reflect the stimuli to which they are being subjected.”
So how much did they spend? In 1910, the total amount a young girl spent in a year was around $556, on shirtwaists, undergarments, suits, hose, boots, and hats (both “street” and “dress”). This was roughly one fourth what they said they would spend “if I had all the money I wished.” See the article for the breakdown, plus interesting comments on clothing and class in 1910.
WHAT IT COSTS A YOUNG GIRL TO BE WELL DRESSED: Actual Facts Given by a Student of Sociology Which Were Obtained from a Class of Young Women in a Private School (PDF)
From April 24, 1910