I'll never trust Howard Stern on etymology again.  Here goes:
30 June 1972, LIFE, pg. 73, cols. 1-4.  "The many faces of the
No. 1 model in the world."  Evelyn Kuhn is "the highest-paid
model in the world," but NO   17 August 1975, NY TIMES MAGAZINE,
pg. 12, cols. 1-2.  "'I'm the biggest model, period'/Great face,
great figure, great  personality, the supergirl next door
insists she's more than just the biggest  _black_ model in the
business."  Alas, Beverly Johnson is merely "supergirl." She
states that she aspires  to become a "millionette."  30 June
1975, NEWSWEEK, pg. 41, col. 2.  "Supermodel _Margaux
Hemingway_...."  3 November 1975, NEWSWEEK, pg. 46, col. 1.  "A
6-foot 1-inch supermodel shouldn't have to go to such lengths to
stop  traffic, so what was fashion star _Veruschka_ up to,
perched on a chair in  the middle of Manhattan's Fifth
Avenue...."  13 March 1978, NEWSWEEK, pg. 57, col. 3.  "But
others see Shelley (Hack) up there with the supermodels, and
Columbia Pictures has decided a pinup poster