She was the creation of illustrator Charles Gibson, a particular idealized woman for the late 19th and early 20th century. According to Wikipedia:
Some people argue that the "Gibson Girl" was the first national standard for feminine beauty. For the next two decades, Gibson's fictional images were extremely popular. There was merchandising of "saucers, ashtrays, tablecloths, pillow covers, chair covers, souvenir spoons, screens, fans, umbrella stands", all bearing her image.
The Gibson Girl was tall, slender yet with ample bosom, hips and bottom in the S-curve torso shape achieved by wearing a swan-bill corset. The images of her epitomized the late 19th- and early 20th-century Western preoccupation with statuesque, youthful features, and ephemeral beauty. Her neck was thin and her hair piled high upon her head in the contemporary bouffant, pompadour, and chignon ("waterfall of curls") fashions. The tall, narrow-waisted ideal feminine figure was portrayed as multi-faceted, at ease and fashionable. Gibson depicted her as an equal and sometimes teasing companion to men.
The Gibson Girl personified beauty, a limited amount of independence, personal fulfillment (she was depicted attending college and vying for a good mate, but she was never depicted as part of a suffrage march), and American national prestige.
I'm not convinced that the Gibson Girl was the first fashion mold for women or that she was seen as the ideal model for women of all racial and ethnic groups. But a mold she certainly was, and one with an extremely small waist and extremely puffy hair:
The following snapshots from the early 20th century show that ordinary women did imitate the Gibson Girl:
As they say at Wikipedia, this post is a stump which could be made into something very interesting by building the obvious connections between fashion and how women in general look and how the same is much less applicable to men and then doing some digging inside the concept.